Global Varicella Vaccine Effectiveness: A Meta-analysis

Abstract

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.a National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia; and b Department of Immunization, Vaccines and Biologicals, World Health Organization, Geneva, Switzerland Dr Marin conceptualized and designed the study, reviewed the articles and collected the data, supervised the analysis, interpreted the data, drafted the initial manuscript, and revised the manuscript; Dr Marti conceptualized the study, reviewed part of the articles, interpreted the data, and reviewed and revised the manuscript; Ms Kambhampati carried out the meta-analyses, interpreted the data, and reviewed the manuscript; Dr Jeram conducted an initial literature review, reviewed part of the articles and collected the data, and reviewed the manuscript; Dr Seward conceptualized and designed the study, reviewed part of the articles, critically reviewed the manuscript, and interpreted the data; and all authors approved the fi nal manuscript as submitted.The fi ndings and conclusions in this report are those of the authors and do not necessarily represent the offi cial position of the Centers for Disease Control and Prevention. For authors affi liated with the World Health Organization, the authors alone are responsible for the views expressed in this publication ...

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“…Alternatively, the addition of a second dose provides protection against all severities [25]. The economics of implementing one- or two-dose schedules have been widely debated [20,26,27], but national choices will ultimately depend on whether their priorities are varicella elimination or prevention of severe disease.…”

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“…Since this recommendation, two-doses of VV have been shown to provide greater protection than one-dose (67), with varicella incidence, hospitalisations, and outbreaks all having declined (230, 231). Over 2.5 years the VE of two-doses of VV in preventing varicella was 98% compared to 86% VE of a singledose, and a relative VE in two versus one-dose recipients of 95% (67), similar findings to a recent meta-analysis of international studies on varicella VE (232).…”

“…A second dose of VV not only reduces risk of infection and interrupts virus transmission (232), it also appears to lower subsequent risk of developing zoster (67). However, the costeffectiveness and incremental benefits of a second-dose needs to be considered in context with funding of all drugs.…”

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