19 Diphtheria Toxoid Tejpratap S.P

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19 Diphtheria Toxoid Tejpratap S.P. Tiwari and Melinda Wharton

Respiratory diphtheria is an acute communicable upper respi- Schick introduced a skin test for immunity that consisted of the ratory illness caused by toxigenic strains of Corynebacterium injection of a small, measured amount of diphtheria toxin; in diphtheriae, a Gram-positive bacillus. The illness is character- immune persons, circulating antibody neutralized the toxin, ized by a membranous inflammation of the upper respiratory and no local lesion was observed.2 The Schick skin test was tract, usually of the pharynx but sometimes of the posterior widely used to distinguish immune individuals and target nasal passages, larynx, and trachea, and by widespread damage immunization to those susceptible. In the early 1920s, Ramon to other organs, primarily the myocardium and peripheral showed that diphtheria toxin, when treated with heat and for- nerves. Extensive membrane production and organ damage malin, lost its toxic properties but retained its ability to produce are caused by local and systemic actions of a potent exotoxin serologic protection against the disease. Thus the current produced by toxigenic strains of C. diphtheriae. A cutaneous immunizing preparation, diphtheria toxoid, came into being.6 form of diphtheria commonly occurs in warmer climates or tropical countries. WHY THE DISEASE IS IMPORTANT HISTORY OF THE DISEASE Before the introduction of diphtheria immunization, diphtheria was a major cause of childhood mortality, and it remains Historical descriptions of diphtheria-like illness (throat mem- endemic in many developing countries. A large outbreak of brane, neck swelling, frequent suffocation) first appeared in diphtheria in the newly independent states of the former ancient Egyptian writings from the second millennium BC1 Soviet Union in the 1990s highlighted the potential for this with increasingly detailed descriptions by Greek writers, ancient scourge to reemerge in countries that fail to maintain including Hippocrates (fifth century BC), Aretaeus (second high levels of population immunity through immunization.7 century AD), and Aëtius (sixth century AD).2–4 Only isolated reports of the disease appeared until the 17th century, when devastating outbreaks occurred in Spain.3 Indeed, in Spanish BACKGROUND history, 1613 is known as the Year of Diphtheria (Año de los Clinical Description Garrotillos).2 Successive outbreaks occurred in southwestern Europe approximately every 12 years through the 18th century. Classic diphtheria has an insidious onset after an incubation The earliest definitive description of diphtheria in America was period of 1 to 5 days (rarely longer). The gradual onset of that of Samuel Bard in New York in 1771, although outbreaks diphtheria is in contrast to the usually sudden, almost explo- had previously been noted in the American colonies.2,3,5 In the sive manifestations of streptococcal pharyngitis. Symptoms of early 19th century, Bretonneau clearly delineated the clinical diphtheria are initially nonspecific and mild; throughout the picture of diphtheria, convincingly argued for its communica- course of the disease, the patient’s temperature usually does bility, successfully pioneered tracheostomy as a method of not exceed 38.5°C. Other early symptoms in children include treatment, and gave the disease its name, derived from the diminished activity and some irritability. At the very onset of Greek word for leather or tanned skin.2,3 symptoms, the pharynx is inspected on examination but no In the second half of the 19th century, increasingly severe membrane is present. About a day after onset, small patches epidemics swept many parts of Europe and the large cities of of exudate appear in the pharynx. Within 2 or 3 days, the the United States, and vigorous efforts were made by research- patches of exudate spread and become confluent and may ers in the new field of bacteriology to identify the causative form a membrane that covers the entire pharynx, including agent.4 In 1883, Klebs first described the characteristic organ- the tonsillar areas, soft palate, and uvula. This membrane isms in stained preparations of diphtheritic membranes, and becomes grayish, thick, and firmly adherent to the underlying Löffler reported the successful growth of these organisms in mucosa. Efforts to dislodge the membrane result in bleeding. culture a year later.3 Other investigators soon confirmed the Anterior cervical lymph nodes become markedly enlarged and pathogenicity of the organism for guinea pigs, and in 1888, tender. In a proportion of patients, the lymph node swelling Roux and Yersin demonstrated the presence of a potent exo- is associated with considerable inflammation and edema of toxin (see “Passive Immunization,” later). Over the next the surrounding soft tissues, giving rise to the so-called bull- decade, antisera produced in animals by injection of sublethal neck appearance, which is associated with a higher morbidity or inactivated cultures were first shown to prevent death in and mortality. Although fever is rarely high, the patient char- nonimmune animals that were challenged with virulent acteristically appears toxic and displays a rapid, thready pulse. organisms, and then to prevent death in children with clinical In untreated patients, the membrane begins to soften about a diphtheria.2,3 week after onset and gradually sloughs off, usually in pieces The concept of active immunization began with Theobald but sometimes as a single unit. As the membrane detaches, Smith in 1907, who noted that long-lasting immunity to diph- acute systemic symptoms, such as fever, begin to disappear. theria could be produced in guinea pigs by the injection of Although pharyngeal diphtheria is by far the most common mixtures of diphtheria toxin and antitoxin and suggested that form of disease seen in unimmunized populations, other skin these mixtures might do the same for humans. After successful or mucosal sites may be involved. Laryngeal diphtheria occurs immunization of children by von Behring with toxin–antitoxin in 25% of cases; in 75% of these instances, the pharynx is also mixtures, immunization programs began in selected European involved. Isolated nasal diphtheria is uncommon (approxi- and American cities. However, these immunizations, although mately 2% of cases). Cutaneous, aural, vaginal, and conjunc- usually effective, were not free of adverse reactions. In 1913, tival diphtheria together account for only approximately 2% 261

Downloaded for Pediatrijas katedra ([email protected]) at Riga Stradins University from ClinicalKey.com by Elsevier on January 18, 2020. For personal use only. No other uses without permission. Copyright ©2020. Elsevier Inc. All rights reserved. 262 SECTION 2 Licensed Vaccines and Vaccines in Development of cases and are often secondary to nasopharyngeal infection. local symptoms of diphtheria in the respiratory tract are resolv- Laryngeal diphtheria may occur at any age, but is particularly ing and the patient is otherwise improving. likely to occur in children younger than 4 years. It is marked In either early or late myocarditis, a wide variety of clinical by an insidious onset with gradually increasing hoarseness and electrocardiographic findings may be noted.24 Tachycar- and stridor. Fever is usually slight. The diagnosis is often dia, distant heart sounds, and a weak pulse may be observed. missed or delayed when the pharynx is not simultaneously Electrocardiography most often shows conduction changes involved. Laryngeal diphtheria is associated with greater and alterations in T waves. Supraventricular and ventricular morbidity and mortality as a result of airway obstruction and ectopic rhythms are common in severe diphtheria, even in the the greater degree of toxin absorption from the extensive absence of evidence of heart failure.26 The earlier electrocar- membrane. diographic changes appear, the worse is the prognosis. Com- Cutaneous diphtheria is an indolent skin infection that plete heart block frequently occurs and is usually fatal; often occurs at sites of burns or other wounds and may act as a ventricular pacing may not improve survival.27–30 Echocardio- source of respiratory infection in others.8–12 It is more common grams show decreased contractility and ventricular dilation in warmer climates and in poor social conditions.8–11 Although proportional to the severity of the clinical carditis; a left ven- sufficient diphtheria toxin is absorbed from skin lesions to tricular ejection fraction of less than 35% is associated with frequently produce immunity, systemic complications are an increased risk for death.31,32 Although electrocardiograms uncommon with cutaneous diphtheria. In warmer climates, and echocardiograms return to normal in most survivors, the high incidence of cutaneous diphtheria appears to have residual changes are seen in some survivors of severe carditis played a major role in producing immunity in the population for up to several years after illness.26,31,33 Left bundle-branch in the absence of high rates of respiratory diphtheria. block at hospital discharge has a poor prognosis.34 Invasive disease caused by C. diphtheriae occurs rarely, Neurologic complications of diphtheria are primarily toxic most commonly as a result of nontoxigenic strains. Bacteremia, peripheral neuropathies, and they occur in approximately endocarditis, osteomyelitis, and arthritis have been reported.13–17 15% to 20% of cases.35,36 The manifestations are more motor Molecular epidemiology studies show that several of the than sensory and usually begin 2 to 8 weeks after onset of the reported clusters of invasive disease were associated with clon- illness. In severe cases, palatal paralysis with consequent nasal ally related organisms.18–20 voice and nasal regurgitation of ingested fluids may occur during the acute membranous phase, particularly with exten- Complications sive pharyngeal disease, and are believed to be attributable to local effects of the toxin. With milder disease, palatal paralysis The impact of diphtheria is largely measured by complica- is common as late as the third week. Symmetric peripheral tions attributable to the local disease and to the effect of neuritis of the lower extremities is a frequent neurologic com- absorbed toxin on other organs. The major threat from laryn- plication, usually occurring 3 to 10 weeks after onset of the geal diphtheria is respiratory obstruction. Life-endangering infection. Diaphragmatic paralysis occasionally occurs, usually obstruction is generally managed by tracheostomy. Even with a month or more after onset, and may require mechanical a tracheostomy tube in place, fatal acute respiratory obstruc- respiratory support. Ocular paralysis, involving either the tion occasionally occurs when a portion of a laryngeal mem- extraocular muscles or those of accommodation, sometimes brane is dislodged and aspirated. The membrane may extend appears, usually 5 or 6 weeks after onset. Fortunately, func- down into the tracheobronchial tree, resulting in pneumonia tional recovery from these neuropathies is the rule, even in and expiratory respiratory obstruction. Because of edema of severe disease.37 An association between diphtheria and the upper respiratory tract, pharyngeal and nasal diphtheria delayed-onset hearing loss has also been reported.38 are frequently associated with secondary otitis media and sinusitis. BACTERIOLOGY The majority of deaths from diphtheria result from the effects of absorbed diphtheria toxin on various organs; severe Corynebacterium diphtheriae is a slender, Gram-positive bacil- complications from toxin absorption include acute systemic lus, usually with one end being wider, thus giving the often- toxicity, myocarditis, and neurologic complications, primarily described club-shaped appearance. On culture, particularly peripheral neuritis. The risk for complications is directly pro- under suboptimal conditions, characteristic bands or granules portional to the extent of local disease, presumably because appear. On smear, the organisms often have a “pick-up sticks” of increased production and absorption of the toxin in larger relationship, assuming parallel (palisade-like), or V- or L-type membranes. In addition, the frequency of these various com- patterns. The organisms are resistant to environmental plications appears to vary considerably between epidemics, for changes, such as freezing and drying. There are four biotypes which no clear explanation is available. In the past, it was of C. diphtheriae (gravis, mitis, belfanti, and intermedius), erroneously believed that the severity of the disease could be which historically were identified by colonial morphology and related to strains of the organism that were morphologically biochemical differences; however, in practice, only the inter- different on culture, being designated gravis, intermedius, and medius biotype can be distinguished reliably by colonial mor- mitis.21,22 A possible explanation for variation in reported fre- phology.39 No consistent differences are found in severity of quency of complications is variability in the timeliness of disease caused by different biotypes. Biotype differentiation is therapy with diphtheria antitoxin, as well as differences in not supported by phylogenetic analyses.40 susceptibility among affected populations. Severe acute systemic toxicity with myocardial involvement PATHOGENESIS AS IT RELATES TO PREVENTION usually occurs between the third and seventh day of the illness; many investigators classify this complication as early myocar- The exotoxin produced by C. diphtheriae is by far the most ditis.23 Others, however, believe that the effects on the myocar- important pathogenic factor associated with the organism. dium are only part of diffuse systemic toxicity, including fever, The extensive study of the biology of diphtheria toxin has purpura, peripheral circulatory collapse, restlessness, somno- pioneered many biomedical developments over the past lence, and disturbances of carbohydrate metabolism.24,25 This century. The basic biology of diphtheria toxin, including its so-called early myocarditis is usually fatal. Late myocarditis production and actions, has become reasonably well under- usually appears in the second or third week of illness, when the stood, although some gaps remain.41,42

The ability of strains C. diphtheriae to produce toxin results type-specific immunity. Lack of immunity to K antigens from a nonlytic infection by one of a series of related bacte- appears to be responsible for the fact that local upper respira- 19 riophages that contain a genetic sequence encoding the toxin. tory tract diphtheria can occur with non–toxin-producing The phage integrates into specific sites present inC. diphtheriae organisms, and toxin-producing organisms may infect persons and other Corynebacterium species. The presence of the phage with ample serum antitoxin levels, but neither of these is thought to confer a survival advantage to the bacterium by instances is associated with systemic manifestations, even increasing the probability of transmission in a susceptible though a faucial membrane is produced.55 Another factor population; transmission may be facilitated by local tissue responsible for the local invasiveness of the organism is the damage resulting from the toxin.43,44 The sequence of diphthe- so-called cord factor, which is a toxic glycolipid. This glyco- ria toxin has been demonstrated to be highly conserved in C. lipid has been shown to disrupt mitochondria, depress cell diphtheriae strains, suggesting that immunologically important respiration, and interfere with oxidative phosphorylation.56 differences among the toxins produced by different strains are The term cord factor is derived from a similar substance found unlikely to occur.45 Once integrated, the tox gene is part of a in Mycobacterium tuberculosis that results in the growth of the multiple bacterial gene operon; other bacterial gene products organism in serpentine coils. Undoubtedly, there are other in this operon are involved in the liberation and uptake of factors as well that help C. diphtheriae establish residence and host iron.46 The entire operon is under the control of a repres- provide nutritional substrates. sor gene, dtxR, which in the presence of iron binds to and Some strains of two other closely related Corynebacterium inhibits the tox gene; toxin is produced only under low-iron species, Corynebacterium ulcerans and Corynebacterium pseudo- conditions.47 tuberculosis, have been demonstrated to produce diphtheria Diphtheria toxin is a polypeptide with a molecular weight toxin,57 and nontoxigenic strains can be converted to toxi- of approximately 58,000 Da. The toxin is secreted as a proen- genic strains by infection with β-corynebacteriophage.58 zyme, requiring enzymatic cleavage into two fragments (frag- Sequencing studies demonstrate that both the base-pair ments A and B) to become active. Fragment B is responsible sequence of the tox genes and the amino acid sequence of the for attachment to and penetration of the host cell. Although diphtheria toxins from C. diphtheriae and C. ulcerans differ by nontoxic by itself, fragment B appears to be the antigen approximately 5%.59 Disease indistinguishable from that responsible for clinical immunity. The receptor domain of caused by toxigenic strains of C. diphtheriae is associated with fragment B binds to a cell surface receptor, heparin-binding C. ulcerans infection.60–63 epidermal growth factor precursor,48 with CD9 as a corecep- 49 tor. After receptor-mediated endocytosis and penetration of DIAGNOSIS the cell, fragments A and B are detached.50 The released fragment A is the toxic moiety, and it acts by inhibiting protein Diphtheria is rare in the United States. However, physicians synthesis, resulting in cell death.44 Unless cell penetration need to be aware of the signs and symptoms that suggest occurs, fragment A is inactive. Differences in the tissue distri- diphtheria. Some developing countries continue to have high bution of the receptor and coreceptors may account for the levels of circulation of toxigenic strains of C. diphtheriae. Some differential effects of diphtheria toxin on different organs.51,52 circulation persists in a few countries of the former Soviet The ability of tox gene–containing bacteriophages to infect Union after a large epidemic in the 1990s,64,65 and until nontoxigenic strains of C. diphtheriae provides a potential recently limited persisting foci were reported in some highly explanation for the fact that, during outbreaks of diphtheria, developed countries.66,67 both toxin-producing and non–toxin-producing strains of the In countries where the disease is endemic, a patient with organism may be isolated on culture surveys. Some evidence confluent pharyngeal exudate should be suspected of having suggests that the introduction of a toxin-producing strain of diphtheria until proven otherwise. The onset is usually gradual C. diphtheriae into a community may occasionally initiate an over the course of 1 to 2 days and is associated with low-grade outbreak by transfer of phage to nontoxigenic strains of the fever. The hallmark of respiratory diphtheria is the presence organism carried in the respiratory tracts of community of pseudomembrane in the pharynx. Although certain clinical inhabitants, rather than a new strain being the responsible characteristics of membranous pharyngitis caused by diphthe- agent.53 ria, such as the color, adherence, and odor of the membrane, On mucous membranes, the toxin causes local cellular can be recognized as being different from other forms of exu- destruction, and the accumulated debris and fibrin result in dative pharyngitis by experienced clinicians, very few physi- the characteristic membrane. More important, absorbed toxin cians in industrialized countries currently have the experience is responsible for remote manifestations affecting various required to base a differential diagnosis on the clinical appear- organs, including, for example, the myocardium, nervous ance of the lesion. system, and kidneys. Because the lethality of diphtheria is Because laryngeal diphtheria usually occurs concomitantly almost entirely determined by the organism’s toxin, clinical with pharyngeal involvement, membranous pharyngitis with immunity depends primarily on the presence of antibodies to stridor should be considered to be diphtheria until proved the toxin. In the presence of small amounts of formaldehyde, otherwise. However, about a quarter of all cases of laryngeal diphtheria toxin loses its attachment and enzymatic activities diphtheria do not display a pharyngeal lesion and therefore while retaining its immunogenicity, thus becoming a toxoid. may often be misdiagnosed. The differential diagnosis includes This process is the basis of active immunization against epiglottitis caused by Haemophilus influenzae type b (Hib), diphtheria. although uncommon in immunized populations, spasmodic Certain cell wall antigens of C. diphtheriae are also thought croup, the presence of a foreign body, or viral laryngotracheo- to contribute to the pathogenesis of the disease in humans. bronchitis. There should be little confusion regarding the first The cell wall contains a heat-stable O antigen, which is found three because the onset and clinical characteristics of each are in all corynebacteria. The cell wall also contains K antigens, well known and are different from diphtheritic croup, which which are heat-labile proteins that differ among strains of C. is ordinarily associated with gradual onset and steady progres- diphtheriae and therefore permit categorization of the organ- sion through hoarseness to stridor during a period of 2 or 3 ism into a number of types.54 The K antigens play two roles in days. Viral laryngotracheobronchitis may be more difficult to relation to humans: first, they appear to be important in the differentiate, and, if diphtheria is suspected for epidemiologic establishment of infection, and second, they produce local or other reasons, laryngoscopy is indicated.

Nasal diphtheria may be difficult to distinguish from many given to hasten clearance of the organism, prevent transmis- other causes of nasal discharge and accordingly is most likely sion, and cease further production of diphtheria toxin.89 to be suspected if the patient has been exposed to diphtheria, Before the availability of antibiotic therapy, convalescent car- such as during an outbreak. Suspicion should be heightened riage of toxigenic organisms was a major problem. Up to 50% if a serosanguineous discharge is present and if the upper lip and 25% of patients continued to harbor the organism 2 and is ulcerated. However, the latter also occurs with streptococcal 4 weeks after onset, respectively. As late as 2 months after infections. Any cutaneous or mucous membrane lesions at onset, reported carriage rates varied between 1% and 8%.3 other sites should be considered suspicious if a membrane is Long-term convalescent carriers were often subjected to tonsil- noted. lectomy, probably with some effect.90 The risk of complications and mortality from diphtheria Treatment with penicillin or erythromycin should be con- are inversely related to the promptness of diagnosis and treat- tinued for 2 weeks. On completion of treatment, patients ment. Thus, it is critical that the diagnosis be considered, should be cultured twice at least 24 hours apart to confirm appropriate clinical specimens be obtained, and a decision elimination C. diphtheriae. Patients who continue to harbor made regarding administration of antitoxin as early as possi- the organism after treatment with either penicillin or erythro- ble in the course of illness. When diphtheria is suspected, mycin should receive an additional 10-day course of oral treatment for the disease should be initiated immediately after erythromycin, and specimens for follow-up cultures should bacteriologic specimens are obtained, without waiting for be obtained on completion of the course.89 Although treat- results. Delay, even for a few hours, may increase the risk of ment with penicillin or erythromycin has no apparent effect complications and death. on the clinical course of the disease, in most instances the Swabs for culture should be obtained under direct visualiza- organism can no longer be recovered on culture within a tion, preferably from the edge or beneath the edge of the mem- week of therapy and subsequent convalescent carriage is thus brane. Directly stained smears are usually grossly misleading uncommon. even in experienced hands and should not be used. Swabs should be inoculated promptly onto tellurite-containing media and onto blood agar.68 Cultures should be incubated promptly EPIDEMIOLOGY and interpreted by an experienced microbiologist. Because not Incidence and Prevalence Data all C. diphtheriae recovered on culture are toxigenic, testing for toxin production must be performed. The modified Elek immu- Active immunization of children with diphtheria toxoid has noprecipitation test for detection of toxin is the standard assay, markedly altered the epidemiology of diphtheria, reducing but it generally requires 24 to 48 hours, and more rapid diphtheria to extremely low levels in both developed countries approaches to toxin detection have been described.69 Many and developing countries that have sustainable and well- laboratories now use a polymerase chain reaction (PCR) assay implemented vaccination programs. However, diphtheria for the detection of the tox gene.70–73 Although this assay can continues to produce substantial childhood morbidity and provide a rapid indication that an isolate may be toxigenic, in mortality in developing countries with incompletely imple- some isolates the tox gene is detected but is nonfunctional.74 For mented childhood immunization programs.91,92 this reason, toxin production in PCR-positive isolates should From 1980 to 2014, only 57 cases of respiratory diphtheria be confirmed by an immunoprecipitation test. PCR can also be were reported in the United States.93–101 The last case in the performed directly on clinical specimens.75 Real-time PCR United States was reported in 2014 in a 17-year-old white assays that detect toxin genes associated with both C. diphthe- female resident of Ohio.101 However, the isolated organism C. riae and C. ulcerans have been developed.76,77 diphtheriae was nontoxigenic. The patient was fully immu- Several approaches to typing of strains of C. diphtheriae as nized. No other family member or close contact was ill. an adjunct to epidemiologic investigations have been devel- The decline of reported cases in the United States was oped. During the 1960s, Saragea and Maximescu78 developed abrupt partially because cutaneous diphtheria ceased to be a system of phage typing and demonstrated considerable diver- nationally notifiable in 1980 (Fig. 19.1). However, improved sity of circulating strains in different countries. Subsequently, childhood immunization in Mexico and other developing the usefulness of molecular typing methods was demonstrated countries as part of the World Health Organization (WHO) in analysis of outbreak-related strains in Sweden79 and the Expanded Programme on Immunization (EPI) beginning in United States.80 Since then, ribotyping,81 pulsed-field gel elec- the late 1970s is likely to have contributed to improved diph- trophoresis,81 and multilocus enzyme electrophoresis82 have theria control in the United States by reducing importations been used for molecular subtyping, as has PCR–single-strand of toxigenic strains. In the mid-1990s, with so little disease conformation polymorphism (SSCP) analysis.83 A rapid ribo- reported in the United States, it seemed likely that toxigenic typing method using PCR-SSCP has been described.84 Ribotyp- strains of C. diphtheriae were no longer circulating in this ing has been used most extensively and standard nomenclature country.93 However, in 1996, surveillance revealed widespread has been developed.85 Multilocus sequence typing also has circulation of the organism in one American Indian commu- been used and appears useful for discriminating reliably nity in the Northern Plains.102 Similarly, although recognized among strains of C. diphtheriae.86 Molecular methods have been cases of diphtheria remain rare, endemic transmission of C. used to characterize the dominant strains of C. diphtheriae diphtheriae has been documented in some native communities associated with the outbreak in the former Soviet Union,81 and in Canada.103–105 Strains from the United States and Canada to document ongoing endemic circulation in certain commu- were assayed by ribotyping and multilocus enzyme electro- nities in the United States and Canada.66,87,88 However, these phoresis and found to be closely related to strains that circu- tests are only available in research laboratories. lated in the same areas during the 1970s and 1980s, suggesting ongoing endemic circulation.66,88 Circulation has also been reported among the aboriginal population in central Austra- TREATMENT AND PREVENTION lia.106 The common denominator in these communities is WITH ANTIMICROBIALS likely to be poverty and crowding. In temperate climates, respiratory diphtheria occurs year- Although diphtheria antitoxin is the mainstay of diphtheria round but most often during colder months, probably because therapy, penicillin or, alternatively, erythromycin should be of the close contact of children indoors. In tropical climates,

1000 51,500 3000 19 Incidence 100 42,500 2500 Mortality 10 Case 34,000 2000 fatality 1 25,500 1500 rate Cases 0.1 17,000 1000 Deaths

0.01 8500 500

0.001 0 0

0.0001 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 Year 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 Year Figure 19.2. Diphtheria cases (solid line) and deaths (dashed line) in England and Wales, 1940–1949. (From Mortimer PP. The diph-

Figure 19.1. Diphtheria incidence in the United States, 1920– theria vaccine debacle of 1940 that ushered in comprehensive child- 2014, and mortality rates, 1920–1980. Years in which no case was hood immunization in the United Kingdom. Epidemiol Infect. 2011;139: reported are plotted with an incidence rate of 0.0001 per 100,000 487–493.) population. Because of the small number of diphtheria deaths since 1980, case fatality rates (CFRs) are unstable and are not shown on Significance as a Public Health Problem this graph. CFRs have varied widely since 1980 because of the small number of cases, but the overall CFR from 1980 to 2010 was 16%. In the past, in the absence of immunization, most people (Data from the Centers for Disease Control and Prevention, Atlanta, acquired immunity to diphtheria as measured by the Schick GA.) test without experiencing clinical diphtheria. Transplacental antibody to diphtheria toxin is present at birth in most infants but declines to nonprotective levels during the second 6 months of life. Thereafter, the proportion of immune children cutaneous diphtheria is more common and is unrelated to (Schick-negative) in unimmunized populations gradually season. increases to 75% or more, presumably as a result of repeated subclinical infection with the organism.118 Risk Groups In the 21st century, it is difficult to comprehend what a major cause of morbidity and mortality diphtheria was in the Unvaccinated or inadequately vaccinated preschool and past. Before 1900, the best data for the United States were school-age children are most often affected by respiratory from Massachusetts. From 1860 to 1897, death rates from diphtheria. Diphtheria is rare in infants younger than 6 diphtheria ranged between 46 and 196 per 100,000 popula- months of age, presumably because of the presence of mater- tion annually, with a median of 78, with the proportion of nal antibody, and rare among adults, especially those living in total deaths attributable to diphtheria ranging from 3% and urban areas, as a result of acquired immunity. Although no 10% annually.119 By 1900, a considerable fall in the death rate differences in diphtheria incidence were noted by sex in the had occurred and continued to decline from 40 to 15 per prevaccine era, an increased risk of diphtheria among women 100,000 over the next 20 years, presumably because of the was reported in several outbreaks among adults in the 1940s therapeutic use of diphtheria antitoxin and, perhaps, other and subsequently; an increase in risk of diphtheria among measures such as intubation. However, even in 1900, more women was observed in Russia and some of the other coun- than half as many deaths from diphtheria were recorded in tries of the former Soviet Union during the outbreaks that the United States as from cancer.119 Several interesting and occurred there in the 1990s.64,107–111 readable histories of diphtheria in the late 19th and early 20th centuries have been published.120–122 Reservoirs of Infection and Modes Excellent data on morbidity, mortality, and case-fatality of Transmission rates for diphtheria were available for the Province of Ontario for 1880 to 1940 and for several Canadian cities for some of Humans are the only natural host for C. diphtheriae. Transmis- those years.123 Mortality from diphtheria exceeded 50 per sion is from person to person, most likely by intimate respira- 100,000 population in most years before the advent of diph- tory and physical contact. The organism is reasonably hardy theria antitoxin. Mortality subsequently declined to approxi- and has been isolated from the environment of persons mately 15 per 100,000 by World War I, although morbidity infected with C. diphtheriae.112–115 Nonetheless, the occurrence rates did not decline. With the widespread use of diphtheria of indirect transmission by airborne droplet nuclei, dust, or toxoid vaccine beginning in the late 1920s in Canada, the fomites has not been established. Evidence of outbreaks disease nearly disappeared.124 caused by contaminated milk and milk products has been At the beginning of the 20th century, diphtheria was a reported.23,115,116 Cutaneous lesions appear to be important in major cause of death of children in the United Kingdom. In transmission under poor social conditions.9,10,117 1934, the diphtheria mortality rate among children was 38.5 The precise microbial events responsible for the transmis- per 100,000. Widespread diphtheria immunization programs sion of diphtheria remain unclear. However, the molecular began there in 1940 and by 1944, it was reduced to 9.2 per epidemiologic data showing clonal identity of bacteria in large 100,000, and by 1949 both morbidity and mortality were numbers of infected people in the outbreaks in Seattle,80 reduced more than 10-fold compared with the period from Sweden,79 and Russia87 strongly suggest that direct spread of 1940 to 1941 (Fig. 19.2).125 toxigenic bacteria from one individual to another is a major Since the introduction of vaccination with diphtheria factor in large epidemics. toxoid, a number of diphtheria outbreaks have occurred in

Downloaded for Pediatrijas katedra ([email protected]) at Riga Stradins University from ClinicalKey.com by Elsevier on January 18, 2020. For personal use only. No other uses without permission. Copyright ©2020. Elsevier Inc. All rights reserved. 266 SECTION 2 Licensed Vaccines and Vaccines in Development industrial countries. During World War II, a major outbreak physicians fears about adverse events, the use of three doses spread throughout western Europe with well over 1 million of Td (diphtheria and tetanus toxoids–adult) instead of DTP cases reported.126,127 The outbreaks spread from Europe to (diphtheria, tetanus, pertussis) in the childhood immuniza- North America. A major outbreak affecting nearly 1% of the tion schedule, and the absence of an adult Td immunization population of Halifax, Nova Scotia, during the winter of program resulted in inadequate population immunity among 1940–1941 was linked to disease imported by Norwegian children and adults. In addition, delayed recognition of cases sailors.128 Another outbreak occurred in Alabama in 1943 and public health response, and changing social conditions among German prisoners of war.129 facilitated spread once the outbreak began.111 In the Russian By the late 1950s, the incidence of diphtheria was markedly Federation, the emergence of an epidemic clone of C. diphthe- reduced in the United States, but disease continued to occur riae biotype gravis was demonstrated.82 The epidemic clone in some other areas. From 1959 to 1970, 5048 cases of diph- was present in Russia as early as 1985, and strains of this theria were reported in the United States, with the highest clonal group have been retrospectively identified in different incidence rates reported in the southeast, south central, and geographic areas of Russia from 1985 to 1987.134 Many cases northern plains states. Incidence rates were 20-fold higher for were also caused by biotype mitis strains as well, especially in Native Americans and sevenfold higher for blacks than for the newly independent states of Central Asia, suggesting that whites.130 microbial factors alone did not account for the epidemic.135 Diphtheria incidence continued to decline (see Fig. 19.1), The Russian epidemic peaked between 1994 and 1995 and and from 1971 to 1981, 853 noncutaneous and 435 cutaneous subsequently was brought under control by increasing immu- cases were reported in the United States.131 Incidence rates nization coverage with diphtheria toxoid among both chil- exceeded 1 per million population in South Dakota, New dren and adults (see later).64,111 Mexico, Alaska, Washington, Arizona, and Montana, and inci- Diphtheria toxoid has been included in the WHO’s EPI dence rates were 100-fold greater for Native Americans than since its inception in 1974. In developing countries, the imple- for whites and blacks.131 During this period, there were seven mentation of the EPI has led to dramatic falls in the global outbreaks with 15 or more cases in the United States.131 From number of reported cases of diphtheria since 1980; however, 1972 to 1982, a large outbreak of predominantly cutaneous marked disparities remain in reported rates between countries. diphtheria occurred among residents of Skid Road in Seattle, Some countries have achieved control of diphtheria compa- Washington.10,80 The Seattle outbreak and most of the other rable to that seen in highly developed countries. In others, outbreaks from 1969 to 1980 were caused by toxigenic strains disease rates have fallen dramatically but sporadic outbreaks of the intermedius biotype, which had previously been uncom- still occur, for example, Thailand,136 India,137–139 Brazil,140 mon; clonality of these strains was suggested by molecular Indonesia,141 and Laos,142 which have recent evidence of wide- epidemiologic studies of strains from outbreaks in Seattle80 spread circulation of toxigenic strains. Low vaccination cover- and the southwestern states.132 age rates and population immunity were reported in the Although diphtheria has become a rare disease in most affected areas in these countries. developed countries, a major epidemic of it began in the Before the WHO EPI began, it was estimated that close to a Russian Federation in 1990 and subsequently spread through- million cases of diphtheria occurred annually in the Third out the countries of the former Soviet Union (Fig. 19.3), with World, with 50,000 to 60,000 deaths.143 From 1980 to 2013, more than 157,000 cases and 5000 deaths reported between reported cases of diphtheria globally decreased from 97,774 to 1990 and 1998.111 A compendium summarizing the knowl- 4680 in 2013 with control of the outbreak in the former Soviet edge gained from this outbreak has been published.133 Union. Approximately 87% of cases worldwide in 2013 were Although the cause of the epidemic was uncertain, it reported from the WHO Southeast Asian region (Fig. 19.4); was multifactorial. Contributing factors included decline in 77% of cases in this region were reported from India.144 childhood vaccination acceptance and coverage, exaggerated Under the EPI, the goal was to achieve 90% or higher immunization rates in 1-year-old children by the year 2000. By this time, it was estimated that the proportion who had received three doses of DTP vaccine (DTP3) had risen from 100,000 negligible levels in the early 1970s to 81% worldwide, with Africa being the lowest at approximately 55%.145 By 2013, global coverage improved to 84% while 79% of the countries 10,000 of the African region reported DTP3 coverage of 80% or more by 1 year of age.144 Some of the regional differences in these data no doubt reflect differences in either the capacity or 1,000 quality of surveillance in member countries. PASSIVE IMMUNIZATION 100 The history of the development of diphtheria antitoxin was reviewed in detail by Andrewes and colleagues.3 In brief, in 10 1888 Roux and Yersin reported their observation that bacteria- free filtrates of broth cultures of C. diphtheriae, when injected into animals, produced all the manifestations of diphtheria 146 1 except for the membranous local lesions. In rapid succes- sion, other advances followed. von Behring showed that 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 inactivated cultures of the organism injected into animals Year subsequently rendered them protected against living cultures.147 Ultimately, von Behring demonstrated the transfer of Figure 19.3. Reported cases of diphtheria, by year, in the Soviet protection from an immunized animal to another unimmu- Union (1965–1990) and in the newly independent states of the nized one by serum, which he named antitoxin. Diphtheria former Soviet Union (1991–2013). antitoxin was first given to a child in 1891, and antitoxin was

120,000 19 SEAR WPR EMR 100,000 AFR EUR AMR 80,000

60,000 Cases of diphtheria 40,000

20,000

1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 Year

Figure 19.4. Reported cases of diphtheria, by year and region, 1980–2013. AFR, African region; AMR, American region; EMR, European region; EUR, European region; SEAR, Southeast Asia region; WPR, Western Pacific region. (From World Health Organization, Department of Vaccines and Biologicals, Vaccine-Preventable Diseases: Monitoring System 2014 Global Summary. http://apps.who.int/immunization_monitoring/ globalsummary/timeseries/tsincidencediphtheria.html.)

commercially produced in Germany in 1892. The use of difficulty in identifying a supplier and maintaining a supply horses for the production of antitoxin began in 1894 and was for domestic use.151,152 As of January 6, 1997, licensed diph- widespread within a few years. The lack of regulated standards theria antitoxin with a valid expiration date was no longer for the production of equine diphtheria antitoxin resulted in available in the United States, and there was no manufacturer the release of contaminated or counterfeit antisera and con- proposed to produce it. However, for treatment of the disease tributed to the development of the predecessors of the present in the United States, the Centers for Disease Control and Center for Biologics Evaluation and Research of the U.S. Food Prevention has a supply of antitoxin that can be distributed and Drug Administration (FDA).148–150 for treatment under an investigational new drug protocol.153 Equine diphtheria antitoxin continues to be used to date. This antitoxin is comparable to the prior U.S. product and may The product is prepared by hyperimmunizing horses with be requested by calling 770-488-7100. diphtheria toxoid and toxin.149 To diminish reactivity from Novel approaches to passive immunity could include the horse serum, current preparations are semipurified by tech- commercial development of human monoclonal antibodies niques that concentrate immunoglobulin G and remove as to diphtheria toxin or the development of recombinant modi- much extraneous protein as possible. There must be at least fied diphtheria toxin receptor molecules to bind diphtheria 500 units of antitoxin per milliliter, and sterility is attained by toxin.154,155 A neutralizing monoclonal antibody of human microfiltration. A cresol derivative is added as a preservative. origin has been developed which completely protected guinea Diphtheria antitoxin is used for the treatment of diphtheria pigs from lethal challenge in an in vivo assay. The monoclonal and occasionally for prevention in exposed persons. Its thera- antibody binds to the receptor-binding domain of diphtheria peutic efficacy is well established, although it is in no way a toxin and blocks the toxin from binding the receptor.156 substitute for prior active immunization with diphtheria toxoid. No antiserum or hyperimmunoglobulin of human Postexposure Use of Antitoxin and Toxoid origin is currently available. Globally, the production and supply of equine antitoxin The value of antitoxin in postexposure prophylaxis is dubious. for human therapeutic use has become increasingly problem- Theoretically, it should be useful in preventing the establish- atic. Almost all industrialized countries that traditionally ment of infection in exposed, susceptible people because the manufactured and supplied antitoxin have ceased production. toxin plays a role in local invasiveness. However, there is no Unavailability of an antitoxin supply increases the likelihood acceptable clinical evidence of prophylactic efficacy; all that of mortality, as highlighted by shortages during the epidemic exist are anecdotes and small, uncontrolled series of experi- in the newly independent states of the former Soviet Union. ments.3 Even if it were effective, antitoxin would be of little With low demand for the product, many manufacturers have use in controlling community outbreaks, because asymptom- left the market, so only a few manufacturers supply diphtheria atic carriers, rather than persons with overt disease, are usually antitoxin to other countries, many of which have reported the major source of transmission.157 For these reasons,

Downloaded for Pediatrijas katedra ([email protected]) at Riga Stradins University from ClinicalKey.com by Elsevier on January 18, 2020. For personal use only. No other uses without permission. Copyright ©2020. Elsevier Inc. All rights reserved. 268 SECTION 2 Licensed Vaccines and Vaccines in Development antitoxin is not recommended for exposed, susceptible name has since been replaced in English usage with the term persons, particularly in view of the high rates of subsequent toxoid. For primary immunization, the toxin-antitoxin prepa- serum sickness and occasional anaphylaxis. The preferred ration was gradually replaced by toxoid in the United States treatment for exposed, unimmunized, asymptomatic persons and Canada during the next 15 years, and elsewhere thereafter. is to obtain a throat culture, begin immunization with a prepa- In 1926, Glenny and coworkers165 found that alum-precipitated ration containing diphtheria toxoid that is appropriate for age, toxoid was more immunogenic, and by the mid-1940s, diph- and institute prophylaxis with erythromycin or penicillin for theria toxoid was combined with tetanus toxoid and pertussis 7 days, during which time the patient must be kept under vaccine as diphtheria and tetanus toxoids and whole-cell per- surveillance for development of symptoms.89 tussis vaccine. Adsorption of all three onto an aluminum salt followed shortly thereafter. It is clear that the immunogenicity of diphtheria toxoid, as well as that of tetanus toxoid, is USE OF ANTITOXIN FOR TREATMENT enhanced by the adjuvant effects of both pertussis vaccine and 166–168 OF DIPHTHERIA the aluminum salt. In recent years, diphtheria and tetanus toxoids with acellular pertussis components (DTaP) Many studies have demonstrated that therapy with antitoxin have been licensed, and various other combinations of DTaP is efficacious in reducing mortality from diphtheria primarily with Hib vaccine, inactivated poliovirus vaccine, and hepatitis by preventing cardiovascular toxicity.4,158 However, only a B vaccine have been developed.169 Combination vaccines have single controlled therapeutic trial is discussed in the litera- been shown to be as comparably immunogenic as the mon- ture.159,160 This nonblinded trial consisted of treating all ovalent preparations. patients admitted on alternate days with antitoxin and com- paring their outcomes with those of patients admitted on Vaccine Constituents nontreatment days. Eight (3.3%) of 242 patients treated with antitoxin died, compared with 30 (12.2%) of 245 control A preservative to prevent antimicrobial growth is required subjects. when diphtheria toxoid is dispensed in multidose vials. Thi- In addition, many observations of the direct relationship merosal, a preservative containing ethyl mercury, has been between mortality and the day of disease when antitoxin was used in vaccines and biologics for this purpose since the administered provide ample evidence of its efficacy. For 1930s.170 Some diphtheria toxoid–containing vaccines con- example, among 3558 patients observed by Ker,158 320 cases taining only trace (<1 µg of mercury) or no thimerosal are of paralysis occurred. There was a strong direct relationship available in single-dose preparations (single-dose vials or pre- between the frequency of postdiphtheritic paralysis and the filled syringes). Diphtheria toxoid is adsorbed onto an adju- number of days between onset of illness and administration vant (most commonly aluminum hydroxide or aluminum of antitoxin. Only 4.8% of 1168 patients developed paralysis phosphate) to improve the immunogenicity of the vaccine. when antitoxin was administered no later than the second day Only adjuvanted diphtheria toxoids are available in the of illness, in contrast to 12.1% of 1375 patients who received United States. antitoxin on the fourth day of the disease or later. Antitoxin is given intramuscularly or intravenously; many Manufacture of Vaccine authorities prefer the intravenous route for at least part of the dose because a therapeutic blood level can be reached more Diphtheria toxoid is produced worldwide in a standard rapidly.161 The entire therapeutic dose should be administered fashion; in the United States, production and testing proce- at one time, and the amount of antitoxin recommended varies dures are specified in the Code of Federal Regulations. Specifi- between 20,000 and 100,000 units. Larger amounts are recom- cally, a strain of C. diphtheriae that is known to produce large mended for persons with extensive local lesions, because the amounts of toxin (such as the Park Williams 8 strain) is grown amount of toxin produced depends on the size of the mem- in a liquid medium conducive to toxin production. After brane. Furthermore, the longer the interval since onset, the appropriate incubation, sterilization is achieved by centrifuga- higher should be the dose of antitoxin. Toxin that has already tion and filtration. After ascertainment of potency, the filtrate entered host cells is unaffected by antitoxin. is incubated with formalin for conversion to toxoid. The product is then further purified and concentrated to achieve the necessary dosage. It is adsorbed onto an aluminum salt, ACTIVE IMMUNIZATION usually aluminum hydroxide or aluminum phosphate. After History of Vaccine Development each step, appropriate tests for potency and sterility are conducted. Toxoid concentration is ascertained by determining After the discovery of diphtheria toxin and the development the content of flocculating units (Lf) in established fashion; of antitoxin in the 19th century, the first successful approach 1 Lf is the amount of toxoid that flocculates 1 unit of a stan- to active immunization was the use of balanced mixtures dard reference diphtheria antitoxin. The purity of diphtheria of toxin and antitoxin, which successfully immunized both toxoids in vaccines currently licensed in the United States is animals and humans after injection.162,163 The combination usually at least 1500 Lf/mg nondialyzable nitrogen; WHO rec- preparation, toxin-antitoxin, was rapidly accepted as an active ommends a similar standard. Toxoid potency is determined immunizing agent. It was widely used in the United States by assays, with different tests currently required by WHO, the beginning in 1914, and was found to protect approximately European Pharmacopoeia, and the FDA.148,171,172 Although 85% of recipients.164 There is little question that the toxin- there are ongoing efforts to harmonize potency testing require- antitoxin preparation developed by von Behring created active ments globally, no single approach has yet been universally immunity against diphtheria, on the basis of the results of adopted. Schick testing and clinical observation, despite the absence of 3 well-controlled studies. Producers In the early 1920s, Ramon treated diphtheria toxin with small amounts of formalin and found that the product Diphtheria toxoid is produced both by large multinational retained most of its immunizing capacity while losing its toxic vaccine companies and by developing country manufacturers, properties.6 Ramon dubbed this preparation anatoxine; this many of which produce vaccine only for domestic use. A 1995

Downloaded for Pediatrijas katedra ([email protected]) at Riga Stradins University from ClinicalKey.com by Elsevier on January 18, 2020. For personal use only. No other uses without permission. Copyright ©2020. Elsevier Inc. All rights reserved. Diphtheria Toxoid 269 assessment of global DTP manufacturing capacity reported 2005, formulations of tetanus and diphtheria toxoids with DTP production by 63 manufacturers in 46 countries. At that acellular pertussis vaccine (Tdap) have been licensed in the 19 time, it was estimated that approximately two-thirds of chil- United States for use in adolescents and adults. Boostrix (Glax- dren received DTP that was manufactured in their own country, oSmithKline) is currently licensed for use in persons 10 years and that more than one-half of the global DTP supply came of age and older, and Adacel (Sanofi Pasteur) is licensed for from developing country manufacturers.173 In 2006, it was use in persons 11 to 64 years of age. These vaccines are licensed estimated that more than 500 million doses of DTP were for use as a single booster vaccination in persons who have produced globally, with many manufacturers producing previously received a primary series of DTP or DTaP. A single vaccine for domestic use only. More than 100 million doses dose of Tdap is recommended by the ACIP in the United States of DTaP are produced as well, with major production by for persons aged 11 years and older, with the preferred timing Sanofi Pasteur and GlaxoSmithKline. at 11 to 12 years of age.178 A dose of Tdap is recommended for women during each pregnancy to provide maternal antibodies Preparations Available, Including Combinations to their newborn for added protection against pertussis until they are eligible to receive their first dose of DTaP.179 Currently in the United States, diphtheria toxoid is available in combination with tetanus toxoid (DT [diphtheria and Dosage and Route tetanus toxoids–pediatric], Td) and in combination with tetanus toxoid and acellular pertussis vaccine (DTaP), as well All products currently in use in the United States are as in other combination vaccines including DTaP; additional administered as a 0.5-mL dose. Preparations containing diph- combination vaccines are available in Europe, Canada, and theria toxoid should always be injected intramuscularly, not Australia that are not licensed for use in the United States. subcutaneously. Globally, diphtheria toxoid continues to be used in combination with tetanus toxoid and whole-cell pertussis vaccine Vaccine Stability (DTP) as well as in other combinations including DTP. The product is available only in adsorbed form in the United Expiration dates for diphtheria toxoid are established through States. the licensing process for each vaccine by national authorities. Since September 2011, DTaP vaccines from two manufac- Preparations containing diphtheria toxoid should be stored at turers are marketed for use in infants in the United States: refrigerator temperatures (2°C to 8°C) but not frozen. If Infanrix (manufactured by GlaxoSmithKline Biologicals and vaccine has been frozen, it should be discarded. distributed by GlaxoSmithKline) and Daptacel (manufactured by Aventis Pasteur Ltd., and distributed by Sanofi Pasteur). Immunogenicity of Vaccine Two pentavalent combination vaccines—a combined DTaP (Infanrix), hepatitis B vaccine, and inactivated polio vaccine Several laboratory assays for diphtheria antitoxin are available. (GlaxoSmithKline) and a combined DTaP, Hib conjugate Vero cell neutralization assays are highly accurate but techni- vaccine, and inactivated polio vaccine (Pentacel, Sanofi cally cumbersome and are available in only a few research Pasteur, Ltd.)—are available for use at 2, 4, and 6 months of laboratories.180 Standard enzyme immunoassays are widely age; Pentacel is also licensed for use for the fourth dose of the available and technically less demanding; these assays gener- series. A DTaP-inactivated polio vaccine combination, KINRIX, ally correlate with results from neutralization assays at is licensed and marketed by GlaxoSmithKline Biologicals for concentrations greater than 0.01 IU/mL.181 Double-antigen use as the fifth dose of the DTaP series at 4 to 6 years of age. enzyme-linked immunosorbent assay (ELISA), double-antigen Another DTaP-inactivated polio vaccine combination, Quadra- delayed time-resolved fluorescence immunoassays, and toxin- cel, was licensed and marketed by Sanofi Pasteur Limited for binding inhibition tests, which are more accurate than stan- active immunization against DTP and poliomyelitis in the dard enzyme immunoassays but technically less demanding United States. A single dose of Quadracel is licensed for use than Vero cell neutralization, have been developed.182,183 in children 4 through 6 years of age as a fifth dose in the DTaP Maternal antitoxin levels do affect the immune response of vaccination series, and as a fourth or fifth dose in the inacti- infants. Diphtheria antitoxin levels greater than 0.1 IU/mL vated poliovirus vaccination (IPV) series, in children who have inhibit the response to active immunization, but no effect is received 4 doses of Pentacel and/or Daptacel vaccine. seen at levels of less than 0.02 IU/mL.184,185 This is more likely The amounts of diphtheria toxoid in the DTaP vaccines to be of significance in areas where C. diphtheriae continues to currently licensed in the United States range from 6.7 to circulate, resulting in high levels of antibody in mothers and 25 Lf/0.5-mL dose. They provide levels of serum antitoxin that their infants. However, it appears that high maternal antibody are considerably lower than those seen after receipt of whole- titers suppress, but do not prevent, adequate responses of cell DTP, probably reflecting the adjuvant effect of the whole- infants to two doses of vaccine, and after the third dose the cell pertussis component.174,175 However, the lower antitoxin suppressive effect is gone.186,187 The half-life of diphtheria anti- levels induced by vaccination with DTaP are probably of no toxin has been estimated to be 30 days.188 clinical consequence, being manyfold higher than protective After three doses of diphtheria toxoid, nearly all infants levels.169 For routine immunization of children, five doses are develop diphtheria titers greater than 0.01 IU/mL.189 Geomet- recommended (at 2, 4, 6, and 15 to 18 months of age and at ric mean titers vary among vaccine preparations, with some school entry before the seventh birthday).176 The fourth dose DTaP products producing significantly lower geometric mean should be administered at least 6 months after the third titers than those observed after vaccination with DTP174; dose.177 however, these differences are unlikely to be clinically signifi- Combined adult formulation tetanus and diphtheria cant. When the toxoid is used for primary immunization of toxoids (Td) are licensed in the United States for use in persons adults, data suggest that nearly all adults develop diphtheria 7 years of age and older. These vaccines are licensed for antitoxin titers greater than 0.01 IU/mL after administration primary vaccination as a three-dose series in previously unvac- of three doses of diphtheria toxoid, and that most develop cinated persons 7 years of age and older, and as a decennial titers greater than 0.1 IU/mL.190 booster for use in adolescents and adults. These products Vaccination with protein conjugate vaccines containing contain reduced amounts of diphtheria toxoid (<2 Lf). Since diphtheria toxoid may result in a booster response to the

Downloaded for Pediatrijas katedra ([email protected]) at Riga Stradins University from ClinicalKey.com by Elsevier on January 18, 2020. For personal use only. No other uses without permission. Copyright ©2020. Elsevier Inc. All rights reserved. 270 SECTION 2 Licensed Vaccines and Vaccines in Development carrier protein in persons who have previously received diph- during the next few months. Among those immunized, the theria toxoid.191 One of the tetravalent meningococcal polysac- monthly incidence of diphtheria fell to 24.5 per 100,000 pop- charide diphtheria toxoid conjugate vaccines currently licensed ulation, about one-seventh of the rate in the unimmunized in the United States (Menactra, Sanofi Pasteur) contains children during that same period (168.9 per 100,000). In approximately six times as much diphtheria toxoid as is con- Britain in 1943, the rate of clinical diphtheria among the tained in the adult formulations of Td vaccine. Simultaneous unimmunized was 3.5 times that among the immunized, and administration of Td and Menactra resulted in much higher mortality was 25-fold greater.127 In an outbreak in Elgin, Texas, geometric mean titers of diphtheria antitoxin than did Td in 1970, only two of 205 fully immunized, exposed elemen- (120.0 IU/mL compared with 8.4 IU/mL); consistent with the tary schoolchildren acquired the disease.205 In contrast, among increase in diphtheria toxoid content, Menactra alone was also 97 children who had received inadequate or no immuniza- substantially more immunogenic than Td alone (46.5 IU/mL tion, a 13% attack rate occurred. compared with 8.4 IU/mL).192 There is also cross-reactivity In a household study during a diphtheria outbreak in San between diphtheria toxoid and CRM197 in protein conjugate Antonio, Texas, in 1970, vaccine efficacy was estimated at only vaccines; the other tetravalent meningococcal polysaccharide 54%.206 However, because index cases were included and conjugate vaccine licensed in the United States, Menveo denominators of exposed individuals were unknown, the data (Novartis Vaccines and Diagnostics), uses CRM197 as the are difficult to interpret. Furthermore, any differences in attack protein carrier. Children receiving meningococcal serogroup rates between immunized and nonimmunized persons might C-CRM197 vaccines develop higher diphtheria antitoxin levels have been blunted by the institution of antibiotic therapy in than are seen in children who did not receive the vaccine.193,194 all members of the household on recognition of a case. Thus, Lack of baseline immunity to diphtheria may result in poor the apparent efficacy of 54% is probably low. In an outbreak 195 antibody responses to vaccines conjugated to CRM197. in Yemen, the protective efficacy of diphtheria toxoid was Although immunologic interference is a potential concern determined to be 87% by the case-control method.116 with simultaneous administration of diphtheria toxoid with The effectiveness of Russian-manufactured diphtheria diphtheria toxoid or CRM197-containing protein conjugate toxoid was evaluated in several case-control studies during the vaccines,196–198 experience to date does not suggest that the epidemic in the former Soviet Union. Three or more doses of immunogenicity of diphtheria toxoid is adversely affected by diphtheria toxoid were demonstrated to be highly effective in simultaneous administration with these vaccines. prevention of diphtheria among children younger than 15 years in a preliminary study in Ukraine in 1992 and a subse- Correlates of Protection quent study performed in Moscow in 1993. In Ukraine, the effectiveness of three or more doses was 98.2% (95% confi- Several lines of evidence suggest that persons with diphtheria dence interval [CI], 90.3% to 99.9%).207 In Moscow, the effec- antitoxin levels of less than 0.01 IU/mL should be considered tiveness of three or more doses was 96.9% (95% CI, 94.3% to susceptible. Ipsen reported results of studies in which rabbits 98.4%), increasing to 99.0% for five or more doses (95% CI, were administered antitoxin and then challenged with intra- 97.7% to 99.6%).208 In addition, administration of a booster venously administered diphtheria toxin; rabbits with a serum dose of diphtheria toxoid within 2 years was shown to decrease level of 0.01 IU/mL were almost completely protected from risk of diphtheria among children 6 to 8 years of age com- death with the standard lethal dose.199 However, higher doses pared with those who had received the last dose 3 to 4, or 5 of toxin required higher serum antitoxin levels for equivalent to 7 years previously.209 Among adults in the Russian Federa- protection. On the basis of studies of diphtheria antitoxin tion, the effectiveness of three or more doses compared with levels early in the course of disease, persons with diphtheria no doses was 70% (95% CI, 10% to 90%).210 Similarly, recent antitoxin levels of less than 0.01 IU/mL appear to be highly vaccination also was found to be highly effective among adults susceptible to disease, and higher levels are generally associ- in Ukraine.211 ated with progressively less-severe symptoms.199–202 Probably Thus, it appears that the effectiveness of diphtheria toxoid no level of circulating antitoxin confers absolute protection; is high but not 100%. However, most reports indicate that the Ipsen reported two cases of fatal diphtheria in patients with disease in previously immunized individuals is milder and antitoxin levels above 30 IU/mL the day after onset of symp- less likely to be fatal.130,131,205,212–214 In Britain in 1943, case- toms.199 Historically, clinical diphtheria was rare among fatality rates in unimmunized children were more than seven- persons with a negative Schick test; the minimal serum anti- fold greater than rates in those who had been immunized toxin level associated with a negative Schick test was approxi- (6.4% versus 0.9%).127 The failure to protect 100% of indi- mately 0.005 IU/mL.203 Overall, the data allow some general viduals on exposure indicates the importance of herd immu- conclusions regarding protective levels in most circumstances. nity in the disappearance of diphtheria from developed An antitoxin level of 0.01 IU/mL is the lowest level providing countries.215 some degree of protection, and 0.1 IU/mL is considered a protective level of circulating antitoxin. Levels of 1.0 IU/mL Duration of Immunity and Protection and greater are associated with long-term protection.204 Both the diphtheria toxoid formulation and the schedule of Efficacy and Effectiveness of Vaccine administration affect the level of diphtheria antitoxin achieved and the duration of protection. Globally, various schedules for No controlled clinical trial of the efficacy of the toxoid in primary immunization of infants are used, but after three preventing diphtheria has ever been conducted. There is, doses of diphtheria toxoid, most children achieve antitoxin however, strong evidence from observational studies to titers greater than the minimally protective level.216 However, support the effectiveness of vaccination. Some evidence of the in the absence of ongoing exposure, immunity wanes over protective efficacy of diphtheria toxoid is provided by observa- time, requiring booster doses of diphtheria toxoid to maintain tions during the Halifax epidemic.128 During the course of this protective antitoxin levels. Longitudinal studies indicate that outbreak, an intense effort was made to administer diphtheria after a period of rapid decline of antitoxin levels, there is a toxoid to previously unimmunized individuals, and the sub- prolonged, slower decline, presumably reflecting the initially sequent incidence of diphtheria in these children was com- activated immune system and half-life of immunoglobulin, pared with the incidence in the unimmunized population followed by a sustained period of less active production of

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Diphtheria Toxoid 271 immunoglobulin.217,218 Both the four-dose schedule used in convalescent phase of illness because clinical infection does the United States, with 15 Lf doses at 2, 4, 6, and 15 months not always induce adequate levels of diphtheria antitoxin. 19 of age, and the three-dose schedule used in Sweden, Denmark, However, vaccination after onset of disease has no role in and Norway, administering 25 Lf doses at 3, 5, and 12 months treatment of diphtheria; diphtheria patients should be of age, resulted in geometric mean levels well in excess of the promptly treated with diphtheria antitoxin (see “Treatment minimally protective level at 48 months of age.219 Similar and prevention with Antimicrobials” earlier). geometric mean levels were found 23 months after dose three was administered as DT (pediatric diphtheria and tetanus Safety toxoids), DTP, or DTaP, with varying diphtheria toxoid con- tents in a two-, four-, and six-dose schedule.218 In 1990, the Common Adverse Reactions. Extensive data on adverse United Kingdom moved to an accelerated schedule, adminis- reactions after administration of currently available prepara- tering DTP at 2, 3, and 4 months instead of at 3, 5, and 9 tions of diphtheria toxoid, adsorbed, are not available because months of age. Although postvaccination geometric mean the toxoid is usually administered in combination with concentrations of diphtheria antitoxin were lower among chil- tetanus toxoid and, in children, with pertussis vaccine as well. dren vaccinated on the accelerated schedule, geometric mean When it is given in combination with pertussis vaccine, local antitoxin levels did not differ at age 4 years among children reactions often are ascribed to the pertussis-containing com- who completed the series at 8 to 13 months, 6 to 7 months, ponent. In several large clinical trials, the reactogenicity of DT or before 6 months of age, suggesting that adequate protection was compared with that of DTaP for primary vaccination of would be maintained until administration of the preschool infants. In general, the frequencies of reported common sys- booster dose.220–222 temic symptoms (temperature of 38°C or higher, crying for 1 Although various schedules for primary immunization hour or longer, irritability, drowsiness, loss of appetite, vomit- appear to provide adequate protection from diphtheria in the ing) and local reactions (redness, swelling, tenderness) after early years of life, in the absence of a booster dose at 4 to 6 vaccination with DT or DTaP were comparable.230–232 In clini- years, protection may not be maintained throughout the cal trials in Sweden and Italy, DT vaccines containing 15 or school-age years. In Sweden, the first booster dose after the 25 Lf of diphtheria toxoid and 3.75 or 10 Lf of tetanus toxoid, primary series is not administered until age 10 years, resulting respectively, were given to more than 7000 infants. The fre- in lower levels of antitoxin among children 5 to 9 years of age quency of temperature of 38°C or higher after any vaccine than is observed in countries administering a preschool-age dose was 35% in the Swedish trial and 9% in the Italian study. booster.223 In one study, 12% of 10-year-old children had Other common systemic symptoms occurred with similar fre- diphtheria antitoxin levels below 0.01 IU/mL before receipt of quencies in the two studies: crying for 1 hour or longer in 5% a booster dose.224 In the Soviet Union, the immunization and 6% of infants, irritability in 67% and 55% of infants, schedule was changed in 1986, delaying the age 6 (years) drowsiness in 54% and 43% of infants, loss of appetite in 22% booster dose to age 9 years. During the diphtheria outbreak and 26% of infants, and vomiting in 15% and 9% of infants. in Russia in the 1990s, receipt of the booster dose at 6 to 8 Redness and tenderness after any vaccine dose were reported years of age was found to decrease the risk of diphtheria in in 42% and 22% of infants in the Swedish trial, respectively, this age group.209 In countries with longstanding childhood and in 19% and 9% of infants in the Italian study, respectively. immunization programs, adults who have neither been The frequencies of marked redness or swelling were substan- exposed to diphtheria nor received booster doses of diphtheria tially lower in both studies, with redness and swelling of 2 cm toxoid may become susceptible to diphtheria as a result of or more reported in only 4% and 6% of infants in the Swedish waning immunity.216 During the outbreak in the former Soviet trial, respectively.230,231,233 The frequency of adverse reactions Union, waning of immunity was thought to contribute to the after DT increased with increasing dose number.232,234 high incidence rate observed among adults. A large proportion Available data suggest that both diphtheria and tetanus of the population of adults, although seronegative, were previ- toxoids contribute to the reactogenicity of Td and DT. Among ously primed by prior immunization or infection with toxi- Swedish medical personnel with a history of receipt of previ- genic C. diphtheriae, as evidenced by development of protective ous primary immunization in childhood, adverse events (local titers after a single booster dose of toxoid.225–228 Although the tenderness and swelling >5 cm, or general discomfort) were immunization histories of the adult patients were difficult to reported by 11% of those who received 2.5 Lf of diphtheria ascertain, the overall population data suggested that many toxoid, compared with 20% of those who received 2.5 Lf of probably had been immune but lost immunity over time. diphtheria toxoid combined with 0.75 Lf of tetanus toxoid, With implementation of booster vaccination for all age groups, documenting the additive effects of the two toxoids.235 Data the outbreak came under control. from several controlled studies suggest that fever and local The experience of this massive epidemic strongly suggests reactions are more common after administration of Td than that sustaining high immunization coverage with a primary after tetanus toxoid alone.236,237 series of diphtheria toxoid among infants and administering In some populations, large numbers of previously primed booster doses at school entry and subsequently throughout persons develop local reactions and fever in response to diph- life are important for maintenance of population immunity.114 theria toxoid, even at low dosages. In a small study of Israeli WHO now recommends that people living in low-endemic or military recruits who had been previously vaccinated in child- nonendemic areas should receive booster doses of diphtheria hood, mild to moderate pain at the injection site was reported and tetanus toxoids approximately 10 years after completing by 38% and severe pain by 20% after receipt of a booster the primary series, and subsequently every 10 years through- dose of 2 Lf diphtheria toxoid without tetanus toxoid; limita- out life.229 tion of abduction was reported by 8%. Systemic symptoms of mild to moderate or severe weakness were reported by Postexposure Prophylaxis and Therapeutic Vaccination 24% and 9%, respectively, and a temperature of 38°C or higher was reported by a single subject (<1%).238 Similarly, a The immunization status of close contacts of diphtheria cases booster dose of 1.5 Lf was administered to 215 university should be assessed, and any contacts found to not be fully up students with prevaccination diphtheria antitoxin levels of to date with diphtheria toxoid immunization should be vac- less than 0.1 IU/mL. Eight percent reported tenderness at the cinated.90 Diphtheria patients should be immunized in the injection site, and 13% reported pain with abduction, which

Downloaded for Pediatrijas katedra ([email protected]) at Riga Stradins University from ClinicalKey.com by Elsevier on January 18, 2020. For personal use only. No other uses without permission. Copyright ©2020. Elsevier Inc. All rights reserved. 272 SECTION 2 Licensed Vaccines and Vaccines in Development was marked in 2% of subjects; none had erythema or swell- percent of children who had been primed with DT reported ing noted on examination.239 redness, 56% reported swelling, and 47% reported itching, With current formulations of diphtheria toxoid, the fre- compared with 23%, 15%, and 21%, respectively, among those quency of reported adverse events varies by prior vaccination who had received DTP.246 In contrast, local reactions did not history, prevaccination diphtheria antitoxin level, and dosage differ among children who had received adsorbed DT for the of diphtheria toxoid administered. Among 123 persons 30 to primary series when they were boosted with either adsorbed or 70 years of age with diphtheria antitoxin levels of 0.05 IU/mL nonadsorbed DT.247,248 or less, adverse events after vaccination were more severe Although local injection site reactions are common, only a among those who received 12 Lf of diphtheria toxoid without small proportion of these reactions are clinically significant. A tetanus toxoid as a booster than among those who received study in the Vaccine Safety Datalink found a rate of medically dosages of 5 Lf or 2 Lf of diphtheria toxoid without tetanus attended local reactions after Td of 3.6 per 10,000 among toxoid, supporting the recommendation to administer reduced persons 9 to 25 years of age. Although infection is an unlikely dosages of diphtheria toxoid to adults.240 A second study in cause of injection site swelling after vaccination, persons with military recruits 18 to 25 years of age, most of whom had medically attended local reactions were frequently prescribed documentation of receipt of a complete primary vaccination antibiotics for cellulitis.249 A similar rate of medically attended series in childhood, also showed no differences in adverse local reactions has been reported after Tdap.250 Because admin- events between dosages of 5 Lf and 2 Lf of diphtheria toxoid istration of the U.S.-licensed tetravalent meningococcal con- when combined with tetanus toxoid.241 A newer study in 180 jugate vaccine Menactra (Sanofi Pasteur) contains a relatively adults evaluated the reactogenicity of DTaP (9 Lf) with Td large amount of diphtheria toxoid and may produce a high (2 IU) and monovalent diphtheria toxoid (2 IU). Although level of diphtheria antitoxin in persons who have previously the proportion of vaccinees with local reactions (e.g., ery- received childhood immunization with diphtheria toxoid– thema, induration, warmth, tenderness) was generally lower containing vaccines, there are at least theoretical concerns among recipients of the monovalent diphtheria toxoid than about administration of Td or Tdap after Menactra.192 Preli- was observed in the other two groups, there was no consistent censure data were not available on adverse events after Td or pattern of increased reactogenicity among recipients of DTaP Tdap administered nonsimultaneously after Menactra; postli- compared with Td.242 censure data are limited but do not suggest that significant Lower diphtheria toxoid content generally results in adverse events result from sequential administration of diph- decreased reactogenicity of booster doses among children. theria toxoid–containing vaccines, including Menactra.250 Among children who had previously received three doses of Similarly, a second U.S.-licensed tetravalent meningococcal DTaP containing 25 Lf of diphtheria toxoid at 3, 4, and 5 vaccine, Menveo (Novartis Vaccines and Diagnostics) contains months of age, booster doses containing varying amounts of CRM197 as the protein carrier; prelicensure evaluation of this antigen and adjuvant were administered as a fourth dose at vaccine found a similarly high proportion of vaccinees report- 15 to 27 months of age. Among 117 children who received ing injection site pain associated with administration of Tdap, vaccine containing a reduced amount of diphtheria toxoid regardless of whether it was given before, simultaneously, or (7.5 Lf) and tetanus toxoid (7.5 Lf compared with 10 Lf), after Menveo.251 there were significant reductions in the proportion of children with redness (27% vs 50%), swelling (18% vs 39%), or pain Rare Adverse Events (17% vs 30%) compared with the frequency in 859 children who received the 25 Lf-containing preparation. A temperature The potential for anaphylaxis exists with any protein antigen, higher than 38°C was also significantly more common in the but has not been attributed to diphtheria toxoid. A recent case group receiving vaccine with higher diphtheria toxoid content series from a food allergy clinic identified eight cases of ana- (27% compared with 18%). A third group of 117 children phylaxis after DTaP or Tdap among children with severe milk received vaccine containing 1.5 Lf of diphtheria toxoid, 10 Lf allergy; the authors hypothesized that the reaction could have of tetanus toxoid, and reduced aluminum adjuvant (0.3 mg, been caused by residual casein.252 This observation has not compared with 0.5 mg); the proportion of children experienc- been replicated in other patient populations. The British ing local reactions was lower than those seen with the 25 Lf National Childhood Encephalopathy Study, designed to vaccine and similar to that seen with 7.5 Lf (28% redness, examine the incidence of brain damage after the administra- 25% swelling, 14% pain), but there was no decrease in the tion of pertussis vaccine, showed a slight but statistically insig- proportion with temperature greater than 38°C (28%).243 nificant excess of acute encephalopathy in the first 7 days after Diphtheria toxoid content of one-fifth the dosage at 4 to 6 a dose of DT.253 It is likely, however, that this excess is attribut- years of age was evaluated in a study of 593 children in able to the induction of inevitable manifestations of preexist- Canada, in which the licensed DTaP-IPV combination ing central nervous system disorders by the systemic effects of (Quadracel, Sanofi Pasteur) (15 Lf) was compared with Tdap DT, as was observed with infantile spasms.254 Newer studies (Adacel, Sanofi Pasteur) (2 Lf). The proportions of children suggest that many cases of encephalopathy after DTP are developing erythema, swelling, pain, and fever were signifi- among children with severe myoclonic epilepsy of infants cantly reduced in the group receiving Tdap with 2 Lf of diph- (Dravet syndrome), a disorder associated with mutations of theria toxoid.244 In the United Kingdom, among children who the gene encoding the sodium channel.255,256 had previously received meningococcal conjugate vaccine con- In 1994, the Institute of Medicine (IOM) reviewed the pos- taining CRM197, there were similar rates of local reactions and sible association between tetanus and diphtheria toxoids and fever among children receiving 30 Lf- and 2 Lf-containing vac- Guillain-Barré syndrome (GBS) or polyneuritis. Of 29 reports cines at ages 3.5 to 5 years.245 identified in the medical literature, most cases were in adults Use of adsorbed vaccine for primary immunization has who had received tetanus toxoids alone (21 cases) or tetanus been reported to result in higher rates of local adverse reactions toxoid and tetanus antitoxin (four cases). Few cases of GBS or after subsequent booster vaccination. A higher incidence of polyneuritis after diphtheria toxoid–containing vaccines have local reactions after booster vaccination with DT was observed been reported. In 1994, the IOM concluded that the evidence among Swedish schoolchildren who received adsorbed DT favored a causal relationship between tetanus toxoid and for primary immunization in infancy compared with those GBS,257 but a more recent report concluded that the evidence who had received nonadsorbed fluid DTP. Seventy-three was inadequate to either accept or reject a causal relationship

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Diphtheria Toxoid 273 between diphtheria toxoid, tetanus toxoid, or acellular 73.5% to 85.9% had protective antibody levels for diphtheria pertussis–containing vaccines and GBS.258 Although there is antibodies (>0.01 IU/mL) even when the booster dose was 19 little evidence to support an independent association between combined or given coadministered with other vaccines such receipt of diphtheria toxoid and GBS, cases of GBS have been as IPV or hepatitis B (HepB).270–272 For added protection reported in the United States among recipients of a tetravalent against pertussis, a dose of Tdap is recommended to replace meningococcal conjugate vaccine, in which the meningococ- one decennial dose Td in persons who have not received a cal polysaccharides are conjugated to diphtheria toxoid (Men- prior dose of Tdap previously. In some industrialized coun- actra, Sanofi Pasteur).259 A causal relationship between receipt tries like the United States, United Kingdom, Canada, New of Menactra and GBS has not been established. Zealand, and Belgium, Tdap is recommended during every pregnancy to protect the newborn against pertussis.273–277 In Indications for Vaccine. DTaP is ordinarily not given to Latin America, Tdap is recommended for use during preg- infants who are younger than 6 weeks of age because responses nancy situations of high risk such as outbreaks.278 to pertussis vaccine in the young infant are suboptimal; Limited data regarding simultaneous administration of the responses to tetanus and diphtheria toxoids, however, are sat- first three doses of DTaP with other childhood vaccines indicate isfactory in such young infants regardless of the presence of no interference with response to the diphtheria toxoid compo- maternally derived serum antibody and without induction of nent. Data are available regarding administration of DTaP with immunologic tolerance.260 The optimal age for immunization other vaccines recommended at the same time as the fourth and of premature infants cannot be stated with confidence, fifth doses of the diphtheria, tetanus, and pertussis series (i.e., although available data suggest that satisfactory responses are Hib conjugate vaccine, measles-mumps-rubella vaccine, and achieved by initiating the usual DTP series according to the varicella vaccine) and regarding administration of whole-cell routine immunization schedule regardless of pregnancy DTP (all doses in the series) with these vaccines.177,279 DTaP may duration.261–264 Follow-up of a small group of children born at be administered simultaneously with other routinely recom- less than 29 weeks’ gestation suggests lower diphtheria anti- mended childhood vaccines, including HepB vaccine, Hib body levels at age 7 years, after a five-dose series, than in vaccine, inactivated poliovirus vaccine, pneumococcal conju- children born at term.265 There is evidence that high titers of gate vaccine, and rotavirus vaccine, to infants at ages 2, 4, or 6 transplacental antibody to diphtheria toxin inhibit serologic months. responses to the first two doses of diphtheria toxoid in infants, As with tetanus toxoid and pertussis vaccine, prolonging but after the third dose (administered in the Swedish schedule the interval between doses does not require restarting the at 12 months of age), the effect is no longer evident.186 series; indeed, immune responses achieved after longer inter- Diphtheria and tetanus toxoids, adsorbed, for pediatric use vals between doses than those recommended are often higher (DT) is recommended for the primary immunization of chil- than after the regular schedule, although the subject may be dren younger than 7 years in whom pertussis vaccine is con- left unprotected in the interim. traindicated. DT contains 10 to 12 Lf of diphtheria toxoid; In other countries, DTP is administered according to infants who begin the series before 1 year of age should receive alternative schedules (see Chapters 72 and 74). According to DT at 2, 4, 6, and 15 to 18 months of age. Satisfactory responses the recommended schedule for the WHO’s EPI, DTP is are obtained even in the absence of the adjuvant effect of administered at 6, 10, and 14 weeks. In a number of Euro- pertussis vaccine.266,267 For unimmunized children 1 to 7 years pean countries, two doses of DTP or DTaP are administered of age, two doses 2 months apart and a third dose 6 to 12 early in the first year of life, followed by a third dose late in months later constitute primary immunization.268 the first year or early in the second year of life. Recommen- Tetanus and diphtheria toxoids, adsorbed, for adult use dations regarding subsequent boosters vary by country. (Td) contains approximately the same amount of tetanus In response to the epidemic of diphtheria in the former toxoid as do DTP and DT, but the amount of diphtheria toxoid Soviet Union, booster doses have been recommended or is reduced to no more than 2 Lf per dose. This reduction reinstated in a number of countries outside the former minimizes reactivity in persons who may have been sensitized Soviet Union. WHO now recommends that the primary vac- previously to diphtheria toxoid, and it is sufficient to provoke cination series of three doses starting as early as 6 weeks of satisfactory anamnestic responses in previously immunized age and with a minimum interval of 4 weeks between doses. persons.216 In addition, in previously unimmunized older chil- Where resources are available, additional doses can be given dren and adults, Td is satisfactory for primary immuniza- after completion of the primary series. In some countries, tion190,269 when administered as a three-dose series, with the additional booster doses are given in the second year of life second dose given 4 to 8 weeks after the first dose, and the and a second booster is given at 4 to 7 years of age. WHO third dose 6 to 12 months after the second dose.262 Td should recommends that people living in low-endemic or nonen- be administered approximately every 10 years after the com- demic areas should receive a booster dose of diphtheria pletion of childhood immunization, with the first booster toxoid approximately 10 years after the primary series and dose given as Tdap. Although Td is slightly more reactive than subsequently every 10 years throughout life to sustain tetanus toxoid alone,235 it is preferable to monovalent tetanus immunity, and that particular attention should be given to toxoid for prophylaxis of tetanus after wounds to maintain revaccination of healthcare workers.229 satisfactory population immunity against diphtheria. In the In some countries, booster doses are administered as adult United States, DT and Td are distributed by Sanofi Pasteur, Inc. formulations of Tdap to some age groups. Monovalent diphtheria toxoid is no longer available in the United States. Contraindications and Precautions Tdap contains a reduced dose of acellular pertussis vaccine and adult formulation diphtheria and tetanus toxoids. Two There are few contraindications to the use of diphtheria toxoid. Tdap vaccines are licensed for use in the United States, with Severe hypersensitivity reactions after a previous dose are con- different age indications (see “Preparations Available, Includ- sidered contraindications to further doses.268 Even though ing Combinations” earlier). Both Tdap products are currently causation by pertussis vaccine is not established, children who licensed for use as a single booster dose. After 10 years of experienced encephalopathy within seven days after adminis- follow-up from receiving Tdap, 97% to 100% of participants tration of a previous dose of DTaP or Tdap vaccine and not had protective levels of tetanus antibodies (>0.01 IU/mL) and attributable to another cause should not receive additional

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Local side effects alone do not preclude continued use. adults, varying from 38% in Azerbaijan to 82% in Latvia Vaccination of persons with severe, febrile illness generally and Lithuania in 1994.290 Before 1986, the last dose of diph- should be deferred until recovery, but mild illnesses with or theria toxoid was routinely administered at 14 to 16 years of without fever should not preclude vaccination. age in the Soviet Union; in response to an increase in Some diphtheria toxoid products are packaged in contain- reported cases of diphtheria in the early 1980s, targeted vac- ers (vials or syringes) containing latex rubber. If a person cination of certain occupational groups was initiated, but reports a severe anaphylactic allergy to latex, vaccines supplied routine use of booster vaccinations among adults was not in vials or syringes that contain natural rubber should not be recommended. Immunogenicity studies in Russia, Ukraine, administered, unless the benefit of vaccination outweighs the the Baltic States, and Georgia demonstrated that some adults risk of an allergic reaction to the vaccine. For latex allergies failed to develop a booster response to a single dose of other than anaphylactic allergies (e.g., a history of contact diphtheria toxoid, suggesting that they may never have allergy to latex gloves), vaccines supplied in vials or syringes received an effective primary series in childhood.225–228,291 that contain natural rubber or natural rubber latex can be Childhood immunization coverage was low in some regions administered.280 in the late 1980s and early 1990s, in part because of an Persons with a bleeding disorder or receiving anticoagulant extensive list of contraindications to vaccination,292 which therapy may receive indicated vaccinations by the intramuscu- undoubtedly contributed to the epidemic.293 For control of lar route if, in the opinion of a physician familiar with the the epidemic, the WHO recommended identification, isola- patient’s bleeding risk, the vaccine can be administered with tion, and appropriate treatment of all cases; prevention of reasonable safety by this route. A fine needle (23 gauge or secondary cases by optimum management of close contacts smaller) should be used for the injection and firm pressure of cases; and rapidly increasing population immunity by applied to the site, without rubbing, for 2 or more minutes. sustaining high coverage among children with four doses of The patient or family should be instructed concerning the risk DTP in all districts and administering a single dose of an for hematoma from the injection.281 age-appropriate formulation of diphtheria toxoid to the entire population.290 By 1997, all countries had made significant progress in immunization of children and adults; the PUBLIC HEALTH CONSIDERATIONS declines in disease incidence were most dramatic in coun- 64 Epidemiologic Effects of Vaccination tries that had achieved high coverage. Diphtheria incidence has continued to decrease. During the period 2000–2009, Despite the relatively low levels of immunity among adults in 7032 cases of diphtheria were reported in the WHO Euro- many countries, diphtheria has remained well controlled in pean Region, with more than 60% of the cases reported most countries with effective childhood immunization pro- from the Russian Federation. During the decade, diphtheria grams. Historically, it has been thought that 70% or more of incidence decreased by more than 95% in the region. By a childhood population must be immune to diphtheria to 2009, only Latvia reported an incidence of greater than 1 prevent major community outbreaks281; the herd immunity case per million population.64 During the period 2001–2013, threshold has been estimated to be 80% to 85%, based on the a total of 65,226 cases of diphtheria were reported from the average age of infection in the prevaccine era.282 Whether an WHO South East Asia Region; approximately 84% were epidemic of a given infectious disease occurs is influenced by from India.65,140 a number of factors other than the proportion of susceptible persons in the population, including the age distribution of Disease Control Strategies: immune and susceptible persons, the extent of mixing of indi- United States and Others viduals and subgroups in the community, and the infectivity and routes of transmission of the organism.215 In countries The primary control strategy for prevention of diphtheria with high rates of childhood immunization against diphthe- globally is routine childhood vaccination with diphtheria ria, it may well be that epidemics do not occur among adults, toxoid as DTP or DTaP. In countries rendered nonepidemic up to half of whom may be susceptible, because the reservoir through high immunization coverage, WHO recommends of disease in the childhood population has been eliminated that the primary vaccination series of three doses be extended and because the strains of C. diphtheriae circulating in the by at least one booster dose, and acknowledges that revaccina- community are less likely to be toxigenic. tion of adults against diphtheria every 10 years may be neces- Serologic studies in Europe and the United States demon- sary to sustain immunity. strate that many adults in these countries remain susceptible In the United States, DTaP, is administered as a five-dose to diphtheria.223,283–289 Differences in seroprevalence among series in childhood followed by decennial booster doses of countries reflect the varied immunization schedules and vac- Td beginning at age 11 to 12 years. For added protection cination coverage among countries, the effect of immuniza- against pertussis, Tdap is now recommended for the booster tion during military service, and the unknown effects of dose at age 11 to 12 years. Td, rather than monovalent tetanus natural exposure to toxigenic C. diphtheriae.141,142,223 Although toxoid, should be used in emergency departments, physi- there is some variability among countries, studies of diphthe- cians’ offices, and other situations in which tetanus-prone ria seroprevalence frequently have demonstrated low levels of wounds are treated.294–296 There are essentially no indications immunity among older adults. In 1996, a serologic study in for monovalent tetanus toxoid at present in the United States England and Wales showed that only 29% of adults age 60 or elsewhere. years and older had diphtheria antitoxin titers of 0.01 IU/mL Epidemiological surveillance to ensure the early detection or greater.290 A similar pattern of susceptibility is seen among of cases should be in place in all countries, and all countries elderly persons in other countries of Western Europe.223 Some should have access to laboratory facilities that can provide studies also demonstrated less susceptibility among males; in reliable identification of toxigenic C. diphtheriae. Rapid public some countries, this may reflect immunization during military health response to a suspected case of diphtheria, with case service.223 investigation to identify the source of infection and other These concerns have been heightened by the epidemic of persons who may have been exposed, can help limit spread of diphtheria in the former Soviet Union. A striking feature of diphtheria.

299 Cost-to-Benefit Information diphtheria toxin, and an animal reservoir does exist for this organism300,301 and thus for the bacteriophage. Given the 19 The costs and benefits of diphtheria toxoid as a component worldwide ubiquity of carriage of C. diphtheriae and the bac- of DTP or DTaP, administered as part of the routine immuni- teriophages implicated in toxin production, prospects for zation series have been evaluated on several occasions. In eradication of diphtheria currently seem remote. Continuing 1997, it was estimated that diphtheria vaccination prevented active immunization with diphtheria toxoid is the key to the almost all the 276,750 diphtheria cases and 27,675 diphtheria control of diphtheria. deaths that were estimated to occur in the absence of vaccination among a simulated birth cohort of 4.1 million children FUTURE VACCINES during the first 15 years of life; both were cost-saving from the societal and healthcare system perspectives.297 A similar analy- New combination vaccines for use in young children built on sis evaluated DTaP as part of the 2001 recommended child- both the DTaP and DTP backbone are under development.302 hood immunization schedule, which also included Hib Alternative approaches to diphtheria immunization in the vaccine, IPV, measles-mumps-rubella vaccine, HepB vaccine, future may include vaccination by the oral303,304 or nasal305 and varicella vaccine. Vaccination of a hypothetical U.S. birth routes or use of a highly purified, less-reactive antigen306–308 or cohort was estimated to result in savings of more than $2 carrier systems309,310 for diphtheria toxoid that would require billion in direct costs and $24 billion in total costs for cases fewer injections. Such products would be particularly useful of diphtheria prevented and was cost saving both in terms of in the developing world, where severe limitations in health- direct costs (benefit-to-cost ratio: 5.3) and from the societal care personnel and financial resources are major barriers. perspective (benefit-to-cost ratio: 16.5).298

References for this chapter are available at ExpertConsult.com. ERADICATION Although no animal reservoir exists for C. diphtheriae, C. ulcerans may carry the β-corynebacteriophage that encodes

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