AMERICAN ACADEMY OF PEDIATRICS Committee on Infectious Diseases Varicella Vaccine Update ABSTRACT. Recommendations for routine varicella vaccine coverage are more than 90% for children 19 vaccination were published by the American Academy of to 35 months of age and more than 95% at school Pediatrics in May 1995, but many eligible children re- entry.6 Varicella deaths and severe morbidity, as well main unimmunized. This update provides additional in- as the societal disruption of children missing 5 to 7 formation on the varicella disease burden before the days of school or child care, have prompted states to availability of varicella vaccine, potential barriers to im- consider requirements for varicella immunization for munization, efforts to increase the level of coverage, new safety data, and new recommendations for use of the school and child care center entry. Several states and varicella vaccine after exposure and in children with the District of Columbia already have such require- human immunodeficiency virus infections. Pediatricians ments, and a number of other states have begun the are strongly encouraged to support public health officials implementation process. Children 12 months of age in the development and implementation of varicella im- or older without documentation of varicella immu- munization requirements for child care and school entry. nization or infection who do not have a contraindi- cation should receive a dose of varicella vaccine im- ABBREVIATIONS. AAP, American Academy of Pediatrics; ACIP, mediately. In addition, special emphasis should be Advisory Committee on Immunization Practices; CDC, Centers placed on immunization of susceptible older chil- for Disease Control and Prevention; CI, confidence interval; VZV, dren and adults, because the likelihood of severe varicella-zoster virus; VZIG, varicella-zoster immune globulin. infection increases with increasing age. aricella vaccine (Varivax, Merck and Com- POTENTIAL BARRIERS TO IMMUNIZATION WITH pany, Inc, West Point, PA) was licensed on VARICELLA VACCINE VMarch 17, 1995, by the US Food and Drug Potential barriers to achieving high rates of vari- Administration for use in healthy persons 12 months cella immunization among children include the fol- of age or older who have not had varicella. Recom- lowing: 1) the misconception that varicella is uni- mendations for vaccine use were published by the formly a mild disease; 2) concerns about vaccine American Academy of Pediatrics (AAP) in May 1995 effectiveness and safety; 3) concerns about waning and by the Advisory Committee on Immunization immunity; 4) concern that universal immunization of Practices (ACIP) in July 1996.1,2 Updated recommen- young children will shift the disease burden to older dations of the ACIP were published in May 1999.3 age groups among whom the disease is more severe; Despite the recommendations, many eligible chil- 5) the stringent storage and handling requirements dren remain unimmunized. Annualized estimates of the vaccine; 6) vaccine availability; 7) inadequate from July 1997 to June 1998 revealed that national insurance coverage; and 8) lack of requirements for varicella vaccine coverage of children 19 to 35 varicella vaccine for licensed child care and school months of age was 34% with wide variations in state entry.7 In addition, there is an inherent lag time and urban areas, ranging from 6% to 52% (Centers between issuance of recommendations and full in- for Disease Control and Prevention [CDC] unpub- corporation of the recommendations into immuniza- lished data, 1999). tion programs. Although some of these issues are no As a result of underutilization of varicella vaccine, longer barriers to immunization with varicella vac- hospitalizations, serious complications, and deaths cine, others remain. attributable to varicella infection continue to occur in 4,5 the United States. To increase vaccine coverage and VARICELLA DISEASE BURDEN reduce the current morbidity and mortality attribut- Varicella is a common, highly infectious disease able to varicella, the ACIP recently recommended that, in the absence of immunization, infects almost that a physician’s diagnosis of varicella, a reliable every person. Before the availability of the varicella history of the disease, serologic evidence of immu- vaccine, approximately 4 million cases occurred an- nity, or receipt of varicella vaccine be required for 3 nually in the United States, resulting in 10 000 hos- enrollment in child care centers and schools. In ad- pitalizations and 100 deaths.5 In the United States, dition, Healthy People 2010 objectives for varicella more than 90% of infections, two thirds of varicella- related hospitalizations, and almost half of varicella- related deaths occur in children.5 In children, vari- The recommendations in this statement do not indicate an exclusive course cella is one of the most important risk factors for of treatment or serve as a standard of medical care. Variations, taking into 8,9 account individual circumstances, may be appropriate. severe, invasive, group A streptococcal disease. Al- PEDIATRICS (ISSN 0031 4005). Copyright © 2000 by the American Acad- though the incidence of disease among adults is low, emy of Pediatrics. the risk of complications and death attributable to 136 PEDIATRICS Vol. 105Downloaded No. 1 January from www.aappublications.org/news 2000 by guest on September 27, 2021 varicella is 10- to 20-fold higher than that for chil- performed to determine the need, if any, for addi- dren. Despite the lower risks of severe morbidity and tional doses of varicella vaccine. mortality among children, the burden of disease is greatest among children since more than 90% of EFFECT OF VARICELLA VACCINE ON cases occur in this age group. Although the incidence EPIDEMIOLOGY OF VARICELLA of disease had been highest among children 5 to 9 There has been concern that use of varicella vac- years of age,10 in the 1990s, the highest incidence is in cine in young children will create a cohort of adults children 1 to 4 years of age.11,12 at risk for serious varicella disease. Currently, fewer than 2% of adults older than 30 years in the United EFFECTIVENESS OF VARICELLA VACCINE States are susceptible to varicella. As the use of vari- Varicella vaccine has been demonstrated to be cella vaccine increases, the circulation of wild-type very effective. Prelicensure, controlled, clinical trials VZV will decrease and the likelihood that children demonstrated varicella vaccine to be 70% to 90% unexposed to natural infection and unimmunized effective for preventing varicella and more than 95% will enter adolescence and adulthood without immu- effective for preventing severe varicella.13,14 A postli- nity will increase. Mathematical models predict that censure study of 148 children performed during an if varicella vaccine coverage in children is more than outbreak of varicella in a child care center in DeKalb 90%, a greater proportion of cases will occur at older County, GA, found that varicella vaccine was 86% ages, but the varicella disease burden will decrease (95% confidence interval [CI], 73%–92%) effective for for children and adults21 (Table 1). However, if im- preventing varicella and 100% (95% CI, 96%–100%) munization rates for young children with varicella effective for preventing moderate to severe disease. vaccine remain relatively low, the number of chil- Varicella was less severe and resulted in fewer days dren who become susceptible adults will increase as of absence from the day care center among immu- will the opportunities for these susceptible adults to nized compared with unimmunized cases.15 Two contract varicella from unimmunized children. more recent studies found that varicella vaccine was Therefore, physicians who withhold varicella immu- 86% (95%CI, 67%–94%) and 84% effective (95% CI, nization from young children because of fear of cre- 60%–94%), respectively, for preventing varicella and ating a cohort of adults at risk for serious varicella 100% effective for preventing severe varicella.16,17 disease may be creating a self-fulfilling prophecy.22 “Breakthrough” disease following exposure to wild- type varicella-zoster virus (VZV) occurs in about 1% COST-BENEFIT OF VARICELLA VACCINE to 4% of vaccinees per year, and the rate does not In recent years, several cost-benefit analyses of seem to increase with length of time after immuni- varicella vaccine programs have been performed23–25 zation.18 “Breakthrough” disease is usually of short (Table 2). In 1994, Lieu and coworkers23 reported the duration and mild with fewer than 50 lesions and results of a cost-benefit analysis of a program that low-grade or no fever. provided varicella vaccine to all children in the United States younger than 6 years. That same year, DURATION OF IMMUNITY Huse and coworkers24 reported the results of a cost- Although there has been concern about waning benefit analysis of a program that provided routine immunity, follow-up evaluations of children immu- varicella immunization to a hypothetical cohort of nized during prelicensure clinical trials in the United 100 000 children in the United States aged 15 months. States revealed protection for at least 11 years, and In 1996, Beutels and coworkers25 reported the results studies in Japan indicated protection for at least 20 of a cost-benefit analysis of a program that provided years.19,20 However, these studies were during a pe- routine varicella immunization to all children in Ger- riod when a substantial amount of wild-type VZV many between 12 and