Global Varicella Vaccine Effectiveness: A Meta-analysis.

CONTEXT Several varicella vaccines are available worldwide. Countries with a varicella vaccination program use 1- or 2-dose schedules. OBJECTIVE We examined postlicensure estimates of varicella vaccine effectiveness (VE) among healthy children. DATA SOURCES Systematic review and descriptive and meta-analysis of Medline, Embase, Cochrane libraries, and CINAHL databases for reports published during 1995-2014. STUDY SELECTION Publications that reported original data on dose-specific varicella VE among immunocompetent children. DATA EXTRACTION We used random effects meta-analysis models to obtain pooled one dose VE estimates by disease severity (all varicella and moderate/severe varicella). Within each severity category, we assessed pooled VE by vaccine and by study design. We used descriptive statistics to summarize 1-dose VE against severe disease. For 2-dose VE, we calculated pooled estimates against all varicella and by study design. RESULTS The pooled 1-dose VE was 81% (95% confidence interval [CI]: 78%-84%) against all varicella and 98% (95% CI: 97%-99%) against moderate/severe varicella with no significant association between VE and vaccine type or study design (P > .1). For 1 dose, median VE for prevention of severe disease was 100% (mean = 99.4%). The pooled 2-dose VE against all varicella was 92% (95% CI: 88%-95%), with similar estimates by study design. LIMITATIONS VE was assessed primarily during outbreak investigations and using clinically diagnosed varicella. CONCLUSIONS One dose of varicella vaccine was moderately effective in preventing all varicella and highly effective in preventing moderate/severe varicella, with no differences by vaccine. The second dose adds improved protection against all varicella.