Declining herpes zoster vaccine effectiveness in adults 60 years and older
Clinical trials have shown that herpes zoster (HZ) vaccine (Zostavax©) efficacy persists for at least 5 years in persons aged ≥60 years. However, duration of protection in general practice settings is unknown.
This cohort study was conducted among community dwelling members of Kaiser Permanente, Southern California (KPSC). The vaccinated cohort consisted of 186,665 KPSC members who were immunocompetent and received HZ vaccine at ≥60 years of age from 01/01/2007 through 12/31/2014. The unvaccinated cohort consisted of randomly-sampled members who were also immunocompetent and matched 3:1 to the vaccinated cohort based on birth date and sex. Unvaccinated persons were assigned the same index dates as the matching vaccinated persons. Both cohorts were followed after the index date and incident herpes zoster was identified by ICD-9 codes (053.XX) from KPSC electronic health record during the study period. Incidence of HZ was compared between two cohorts and the hazard ratios (HRs) and 95% confidence interval (CI) were estimated, adjusting for sex, race, healthcare utilization, and chronic diseases using Cox proportional hazards regression models.
The number of HZ cases among vaccinated and unvaccinated persons was 4841 in 617837 person-years (7.8 per 1,000; 95% CI, 7.6-8.1 per 1,000) and 19293 in 1318326 person-years (14.6 per 1,000; 95% CI, 14.4-14.8 per 1,000), respectively. The 84-month cumulative risk of HZ in the vaccinated and the unvaccinated was 5.95% and 9.39%, respectively. In adjusted analysis, vaccination was associated with a reduced risk of herpes zoster (HR=0.49; 95% CI, 0.47-0.50); this reduction occurred in all age strata and among those with chronic diseases. The adjusted HR by year after vaccination increased from 0.30 (CI = 0.28-0.32) in the first year after vaccination to 0.71 (CI = 0.61-0.81) in the 6th year. The 95% CIs around the HR point estimates for the 7th year (0.90) and the 8th year (0.76) both included zero.
Preliminary analysis shows that among immunocompetent adults 60 years of age and older, effectiveness of HZ vaccine declined over 7 years of follow-up. Continued follow up of this study population will allow evaluation of long term effectiveness.
H. F. Tseng,
C. Hales, None
S. R. Bialek, None
R. Harpaz, None
S. Tartof, None
L. S. Sy, None
S. Jacobsen, None