AMERICAN ACADEMY of PEDIATRICS Smallpox Vaccine
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AMERICAN ACADEMY OF PEDIATRICS POLICY STATEMENT Organizational Principles to Guide and Define the Child Health Care System and/or Improve the Health of All Children Committee on Infectious Diseases Smallpox Vaccine ABSTRACT. After an extensive worldwide eradication period of 7 to 17 days (mean: 12 days), the period of program, the last nonlaboratory case of smallpox oc- infectivity begins as an enanthema and a rash char- curred in 1977 in Somalia. In 1972, routine smallpox acterized by maculae progressing to papules, vesi- immunization was discontinued in the United States, cles, and pustules all in the same stage, developing and since 1983, vaccine production has been halted. first on the face and extremities. Patients remain Stockpiled vaccine has been used only for laboratory contagious until the scabs have been shed. Most researchers working on orthopoxviruses. In recent years, there has been concern that smallpox virus stocks may be patients are sick enough during the prodromal pe- in the hands of bioterrorists, and this concern has been riod to be confined to bed by the time the rash heightened by the terrorist attack on the World Trade develops. For this reason, household contacts, hospi- Center and the Pentagon on September 11, 2001. Because tal workers, and other health care professionals are most of the population is considered to be nonimmune, the most likely individuals to develop secondary there is debate as to whether smallpox immunization cases. should be resumed. This statement reviews the current status of smallpox vaccine, the adverse effects that were associated with smallpox vaccine in the past, and the OUTCOME, TREATMENT, AND PROTECTION major proposals for vaccine use. The statement provides Case fatality rates of 30% or higher were observed the rationale for a policy based on the so-called ring during epidemics of smallpox. Death, when it oc- vaccination strategy recommended by the Centers for curred, was usually a result of viral toxemia associ- Disease Control and Prevention, in which cases of small- pox are rapidly identified, infected individuals are iso- ated with circulating immune complexes. The more lated, and contacts of the infected individuals as well as discrete and sparse the lesions, the better the prog- their contacts are immunized immediately. nosis. Four forms of smallpox are recognized. In addition to typical smallpox (more than 90% of cases), there ABBREVIATIONS. HIV, human immunodeficiency virus; CDC, are 2 forms of variola major, hemorrhagic (character- Centers for Disease Control and Prevention; VIG, vaccinia im- mune globulin; AAP, American Academy of Pediatrics. ized by hemorrhage into skin lesions and dissemi- nated intravascular coagulation) and malignant or SMALLPOX: THE DISEASE flat type (in which skin lesions do not progress to the mallpox is a highly contagious infection caused pustular stage but remain flat and soft). Each variant by the DNA virus variola, a member of the occurred in 5% of cases and was associated with a genus Orthopoxvirus. As recently as 1967, mil- 90% to 100% mortality rate. Variola minor, or S alastrim, is associated with a longer incubation pe- lions of smallpox cases per year were reported in Asia and Africa. The last known nonlaboratory case riod, a milder prodromal period, fewer skin lesions, of smallpox occurred in 1977 in Somalia and signaled and a lower mortality rate than variola major or 1 the end of a successful worldwide, decade-long erad- typical smallpox. ication effort. The United States discontinued routine In the absence of preexisting immunity, a favor- childhood immunization against smallpox in 1972 able prognosis is less likely for infants, the elderly, and routine immunization of health care profession- and pregnant women. Immunodeficiency, whether als in 1976. In 1980, the World Health Organization from immunosuppressive therapy or from human declared that smallpox had been eradicated success- immunodeficiency virus (HIV) infection, is likely to fully worldwide. have a negative impact on prognosis. Smallpox is spread most efficiently in droplets or Secondary bacterial infections of the skin, eyes, aerosols from the oropharynx of infected individu- and respiratory tract can develop and lead to septi- als. Smallpox also can be spread by direct contact cemia and disseminated bacterial disease. Laryngeal with infected lesions or with clothing or bed linens lesions can lead to edema and airway obstruction. contaminated with the virus. After an incubation Encephalitis also may complicate smallpox. Protection from infection was provided in the past by immunizing all children beginning at 1 year of PEDIATRICS (ISSN 0031 4005). Copyright © 2002 by the American Acad- age. An individual’s concentration of neutralizing emy of Pediatrics. antibodies declines significantly over a 5- to 10-year Downloaded from www.aappublications.org/news by guestPEDIATRICS on September Vol. 29, 1102021 No. 4 October 2002 841 period, and people who were immunized as infants virus stimulates an immune response that cross-re- or children before 1972 are unlikely to remain fully acts with variola and protects the vaccine recipient. protected against disease, but protection against Smallpox vaccine was last used in the general pop- death afforded by antibodies and cell-mediated im- ulation in the United States in 1971. At that time, the munity may persist for 30 years. risk of serious adverse effects from immunization There is no known effective antiviral agent to treat was judged to be greater than the risk of exposure to smallpox, although there is speculation that cidofo- smallpox, the last nonlaboratory US case of which vir may offer some benefit. Infected patients should occurred in 1949.6 In 1983, distribution of the vaccine receive supportive care, including hydration and to civilian populations was discontinued, and vac- treatment of secondary bacterial infections, when ap- cine production was stopped. Since 1990, when im- propriate. Contacts of infected persons should be munization of military personnel ended, smallpox immunized against smallpox within 3 to 4 days after immunization has been recommended only for lab- exposure. This postexposure immunization provides oratory workers at risk of exposure to orthopoxvi- substantial protection against disease and especially ruses and for researchers using vaccinia virus. Re- against a fatal outcome. sponse teams from the Centers for Disease Control and Prevention (CDC) with special expertise in CURRENT CONCERN ABOUT SMALLPOX smallpox management were immunized in 2001.7 Stocks of smallpox virus were retained in govern- The vaccine also has been given to adult volunteers ment-run laboratories in the United States and the specifically for the purpose of determining whether former Soviet Union. There are reports that, before stored vaccine and diluted vaccine retain immuno- the dissolution of the Soviet Union, smallpox was genicity.8,9 being developed as a weapon of biological war- fare.2,3 In addition, decreasing financial support for EFFECTS AND RISKS OF IMMUNIZATION TO Russian government laboratories in recent years led PREVENT SMALLPOX to concern that the virus and the expertise to prop- Immunization causes a local infection that is pru- agate a large amount of smallpox virus may have ritic and uncomfortable. Fever, malaise, and regional fallen into non-Russian hands. The rapidity with lymphadenitis often occur about a week after immu- which smallpox could spread in the US population nization. The site of immunization develops a papule has led to concern that this agent would present a that matures into a pustule and then a scab that particularly potent threat if it were used as an agent separates by about the third week after immuniza- of bioterrorism.4,5 At this time, there are no validated tion. Reimmunization typically causes a milder le- estimates of the chance of smallpox being introduced sion that develops more quickly. Occasionally, satel- into the US population, but many bioterrorism ex- lite or distant pustules develop when a vaccine perts consider it to be quite unlikely. recipient scratches the pustule and autoinoculates the virus at another site. SMALLPOX VACCINE A major reason not to initiate universal immuni- Smallpox vaccine is associated with the early his- zation in the absence of actual cases of smallpox, tory of immunization. In 1798, Edward Jenner re- besides the limited availability of vaccine, is the risk ported that inoculation with cowpox virus protected of serious complications of immunization. Severe people from smallpox. The only smallpox vaccine complications of immunization include death, post- currently available in the United States is a live-virus vaccinal encephalitis, progressive vaccinia, eczema preparation. The vaccine does not contain variola but vaccinatum, generalized rash, and accidental inocu- contains a related virus, vaccinia, which is distinct lation to the face, eye, or other sites (see Table 1). from the cowpox virus used by Jenner for immuni- Smallpox vaccine has been known for decades to zation. The current vaccine is inoculated into the produce significant adverse effects, especially in im- deltoid area or lateral area of the lower leg using a munocompromised persons. In patients with chronic bifurcated needle with a series of jabs that force a skin conditions, smallpox vaccine can cause a severe, drop of the material beneath the epidermis. Success- sometimes fatal dermatologic involvement termed ful immunization is evident by development of a “eczema vaccinatum.”