The United States (US) was the first country to introduce a universal one-dose childhood varicella vaccination program in 1996. The policy was changed to a routine two-dose program in 2006. We describe the two decades of US experience with varicella vaccination.
Review of articles published during 1996-2016 identified by PubMed search for the terms varicella, varicella vaccine, and herpes zoster. The search was limited to US data.
One dose of varicella vaccine is ~82% effective in preventing disease of any severity, 100% effective in preventing severe varicella, and has an excellent safety profile. By the end of the ten years of one-dose vaccination program, high vaccine coverage was attained among children aged 19-35 months (89% nationally, range 76%-96% by state). Consequently, decreases were documented in varicella incidence (83%-90%), hospitalizations (75%-88%), deaths (87%), and direct inpatient and outpatient medical expenditures; declines occurred across all age groups with the largest seen among persons aged <20 years. Continuing outbreaks in schools with high one-dose vaccination coverage prompted adoption of a two-dose policy. The second dose improves protection against varicella of any severity (effectiveness ~92%). Further declines in morbidity occurred after implementation of the two-dose program; by 2014 incidence declined 93%-97% and by 2012 hospitalizations declined 93%, compared with pre-vaccine years. The two-dose program reduced the number, size and duration of outbreaks compared with the one-dose program. For herpes zoster, incidence is lower among one-dose varicella vaccinated as compared with unvaccinated children, and there is no evidence that the vaccine is contributing to changes in the epidemiology of herpes zoster among adults.
The one-dose vaccination program significantly reduced varicella morbidity and mortality. The two-dose program has provided additional disease reduction. Future challenges include developing tools to measure vaccine-induced immunity and monitor its duration, understanding correlates of protection, improving diagnostics for varicella in vaccinated persons, and monitoring herpes zoster epidemiology.
J. Leung, None
D. S. Schmid, None
R. Harpaz, None