Strong Additional Effect of a Second Varicella Vaccine Dose in Children in Germany, 2009-2014

Objectives Vaccine effectiveness (VE) of 1 and 2 varicella vaccine doses in children aged 1-4 years in Germany was evaluated to determine the additional effect of a second dose recommended at least 4 weeks after the first dose and before the second birthday. Study design To estimate the VE, the proportion of cases vaccinated was compared with the proportion of the population vaccinated using nationwide sentinel surveillance data from 2009-2014 and health insurance claims data covering the period January 2009-March 2014, respectively. A general linear model was used to estimate the OR of vaccination in the cases and the population and the corresponding CIs to observe the stability of the VE estimates over time, and to assess the incremental effectiveness of a second dose. Results The overall VE after 1 dose was 86.6% (95% CI: 85.2-87.9), ranging between 94.6% (95% CI: 87.9-97.6) in the first quarter of 2011 and 50.3% (95% CI: 7.3-73.4) in the third quarter of 2013. The overall VE after 2 doses was 97.3% (95% CI: 97.0-97.6), ranging between 99.5% (95% CI: 97.8-99.9) in the second quarter of 2009 and 91.3% (95% CI: 85.7-94.8) in the third quarter of 2013. The incremental VE of 2 doses was 84.6% (95% CI: 81.7-86.9). Conclusions The substantially higher VE of 2 varicella vaccine doses compared with 1 dose in young children and the strong additional effect of the second dose support the public health relevance of a 2-dose schedule and the success of the early second vaccine dose.