Prevention of Varicella: Recommendations for Use of Varicella Vaccines in Children, Including a Recommendation for a Routine 2-Dose Varicella Immunization Schedule

Abstract

National varicella immunization coverage using the current 1-dose immunization strategy has increased among vaccine-eligible children 19 through 35 months of age from 27% in 1997 to 88% by 2005. These high immunization rates have resulted in a 71% to 84% decrease in the reported number of varicella cases, an 88% decrease in varicella-related hospitalizations, a 59% decrease in varicellarelated ambulatory care visits, and a 92% decrease in varicella-related deaths in 1-to 4-year-old children when compared with data from the prevaccine era. Despite this significant decrease, the number of reported cases of varicella has remained relatively constant during the past 5 to 6 years. Since vaccine effectiveness for prevention of disease of any severity has been 80% to 85%, a large number of cases of varicella continue to occur among people who already have received the vaccine (breakthrough varicella), and outbreaks of varicella have been reported among highly immunized populations of schoolchildren. The peak age-specific incidence has shifted from 3-to 6-year-old children in the prevaccine era to 9-to 11-year-old children in the postvaccine era for cases in both immunized and unimmunized children during these outbreaks. Outbreaks of varicella are likely to continue with the current 1-dose immunization strategy.After administration of 2 doses of varicella vaccine in children, the immune response is markedly enhanced, with Ͼ99% of children achieving an antibody concentration (determined by glycoprotein enzyme-linked immunosorbent assay) of Ն5 U/mL (an approximate correlate of protection) and a marked increase in geometric mean antibody titers after the second vaccine dose. The estimated vaccine efficacy over a 10-year observation period of 2 doses for prevention of any varicella disease is 98% (compared with 94% for 1 dose), with 100% efficacy for prevention of severe disease. Recipients of 2 doses of varicella vaccine are 3.3-fold less likely to have breakthrough varicella, compared with those who are given 1 dose, during the first 10 years after immunization.To achieve greater levels of immunity with fewer serosusceptible people, greater protection against breakthrough varicella disease, and reduction in the number of outbreaks that occur nationwide among school-aged populations, a 2-dose varicella immunization strategy is now recommended for children Ն12 months of age. All clinical reports from the American Academy of Pediatrics automatically expire 5 years after publication unless reaffirmed, revised, or retired at or before that time.The guidance in this report does not indicate an exclusive course of treatment or serve as a standard of medical care. Variations, taking into account individual circumstances, may be appropriate.

Influence of Age and Nature of Primary Infection on Varicella‐Zoster Virus–Specific Cell‐Mediated Immune Responses

“…Our observation is also consistent with the higher incidence of varicella break-through disease in vaccine recipients, compared with the extremely low incidence of secondary cases of varicella after wild-type VZV infection [30, 32]. To address the varicella break-through issue, the childhood vaccination schedule currently includes a second dose of varicella vaccine at 5 or 6 years of age [33]. …”

Varicella: epidemiological aspects and vaccination coverage in the Veneto Region

“…In the absence of universal childhood vaccination programme, varicella incidence peaks in children under 10 years of age, with the highest incidence rates between 3 and 6 years of age [7]. …”

An Outbreak of Varicella among Schoolchildren in Taipei

“…In addition, we should solve the problems of sick children without vaccination and parents' misconception about vaccination in order to promote high vaccination coverage. However, even with high vaccination coverage, one dose varicella vaccination did not provide sufficient herd immunity levels to prevent community transmission [19,20]. A second dose of varicella vaccine could increase vaccine effectiveness and decrease breakthrough rate [21].…”

“…A second dose of varicella vaccine could increase vaccine effectiveness and decrease breakthrough rate [21]. A 2-dose varicella vaccine schedule has been recommended for children in United States since 2006 [19]. However, one study showed the vaccine effectiveness of 1 and 2 doses were similar [22].…”