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Declining Effectiveness of Herpes Zoster Vaccine in Adults Aged ≥60 Years. Understanding long-term effectiveness of herpes zoster (HZ) vaccine is critical for determining vaccine policy. 176 078 members of Kaiser Permanente ≥60 years vaccinated with HZ vaccine and three matched unvaccinated members were included. Hazard ratios and 95% confidence intervals (CIs) associated with vaccination at each year following vaccination were estimated by Cox regression model. The effectiveness of HZ vaccine decreased from 68.7% (95% CI, 66.3%-70.9%) in the first year to 4.2% (95% CI, -24.0% to 25.9%) in the eighth year. This rapid decline in effectiveness of HZ vaccine suggests that a revaccination strategy may be needed, if feasible.