Background: Zostavax™, a live zoster vaccine, was licensed in the U.S. in 2006 for the prevention of herpes zoster (HZ) in people over 60 (60+) years, and extended to 50+ in 2011. Vaccine effectiveness (VE) and duration of protection are being evaluated in a long-term observational study, planned to continue through 2024. We previously reported that VE to prevent HZ was high in the 1st year, decreased in the 2nd year and then waned slowly, for an average VE of 45-50% over the first 5 years following a single dose of vaccine in all 60+ age groups. We present here VE against PHN through 2013.
Methods:The study is conducted at Kaiser Permanente Northern California (KPNC) as an open cohort that KPNC members enter when they become age-eligible for the vaccine. PHN cases were identified in the databases within a year of HZ onset as having a PHN-specific diagnosis code >90 days after the first HZ diagnosis code, either (1) for both a visit and a prescription (positive predictive value [PPV] ~96%) or (2) as a primary code for a visit (PPV ~89%). VE against PHN by age at vaccination and by year since vaccination was estimated using Cox regression adjusted for sex, year of birth, race/ethnicity, and several time-varying variables, including healthcare use, comorbid conditions and immune-compromise status.
Results: From Jan-2007 to Dec-2013, over 1.3 million study individuals 50+, including >300,000 who received one dose of Zostavax, contributed ~4.9 million person-years of follow-up and experienced ~42,000 HZ episodes and 1,720 PHN episodes. As of 2013, vaccine coverage was >40% in 60+. VE against PHN was 83% (95% CI 73-90%) in the first year for all ages combined, decreased in the second year, and then remained relatively stable through year 5, with an overall VE of ~70% in all 60+ age groups (60-69, 70-79, and 80+ years at vaccination). Among people vaccinated at 80+, overall VE against PHN was 71% (54-82%).
Conclusion: Overall VE of live zoster vaccine against PHN was ~70% in all 60+ age groups, with less waning over time than seen with VE against HZ. VE against PHN and HZ in people vaccinated at 80+ was similar to younger 60+ groups with a similar trajectory over time. These results support the recommendation to vaccinate all eligible people, including the elderly, who are at increased risk of HZ and PHN.