Effectiveness of the herpes zoster vaccine Zostavax® in Stockholm County, Sweden

Objective: The objective of this study was to estimate the effectiveness of the herpes zoster vaccine Zostavax in a cohort of vaccinated individuals in Sweden. Methods: The study is a retrospective population-based matched cohort study conducted with data from health care registers in Stockholm Country. Primary endpoints were new diagnosis of HZ after administration of Zostavax. Individuals above the age of 50 years and living in Stockholm County in 2013 were included into the study. Ten non-vaccinated individuals per vaccinated were included and randomized into the cohort. The non-vaccinated were matched on age at index date and gender. Results: Zostavax had an overall effectiveness (VE) of 34% (HR = 0.66, 95% Cl: 0.55-0.78). When stratifying by age, 61-75 years was the only age group that showed a reduced risk of HZ (HR = 0.57; CI 0.44-0.73) compared to those that were non-vaccinated. As compared to the unvaccinated group, the VE was significant at days 180-359 (HR = 0.53; 95% CI 0.33-0.88), 360-539 (HR = 0.46; 95% CI 0.27-0.80) and at days 540-719 (HR = 0.56; 95% CI 0.35-0.90) after vaccination. Conclusion: This is the first population-based study in Sweden studying the effectiveness of HZ vaccination. Our findings are well in-line with previous studies, however studies addressing the longitudinal efficacy and effectiveness of Zostavax are still required. (C) 2019 The Authors. Published by Elsevier Ltd.