CONTEXT: Approximately 1 million episodes of herpes zoster occur annually in the United States. Although prelicensure data provided evidence that herpes zoster vaccine works in a select study population under idealized circumstances, the vaccine needs to be evaluated in field conditions. OBJECTIVE: To evaluate risk of herpes zoster after receipt of herpes zoster vaccine among individuals in general practice settings. DESIGN, SETTING, AND PARTICIPANTS: A retrospective cohort study from January 1, 2007, through December 31, 2009, of individuals enrolled in the Kaiser Permanente Southern California health plan. Participants were immunocompetent community-dwelling adults aged 60 years or older. The 75,761 members in the vaccinated cohort were age matched (1:3) to 227,283 unvaccinated members. MAIN OUTCOME MEASURE: Incidence of herpes zoster. RESULTS: Herpes zoster vaccine recipients were more likely to be white, women, with more outpatient visits, and fewer chronic diseases. The number of herpes zoster cases among vaccinated individuals was 828 in 130,415 person-years (6.4 per 1000 person-years; 95% confidence interval [CI], 5.9-6.8), and for unvaccinated individuals it was 4606 in 355,659 person-years (13.0 per 1000 person-years; 95% CI, 12.6-13.3). In adjusted analysis, vaccination was associated with a reduced risk of herpes zoster (hazard ratio [HR], 0.45; 95% CI, 0.42-0.48); this reduction occurred in all age strata and among individuals with chronic diseases. Risk of herpes zoster differed by vaccination status to a greater magnitude than the risk of unrelated acute medical conditions, suggesting results for herpes zoster were not due to bias. Ophthalmic herpes zoster (HR, 0.37; 95% CI, 0.23-0.61) and hospitalizations coded as herpes zoster (HR, 0.35; 95% CI, 0.24-0.51) were less likely among vaccine recipients. CONCLUSIONS: Among immunocompetent community-dwelling adults aged 60 years or older, receipt of the herpes zoster vaccine was associated with a lower incidence of herpes zoster. The risk was reduced among all age strata and among individuals with chronic diseases.
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