The association between herpes zoster vaccination and the decreased risk of dementia: A systematic review and meta-analysis of cohort studies

Background Herpes zoster (HZ) infection may increase the risk of dementia, that causes a heavy socioeconomic burden. However, the epidemiological evidence between HZ vaccination and the risk of dementia remains inconclusive. Objective This meta-analysis was conducted to investigate the effect of HZ vaccination on the onset of dementia. Methods We searched PubMed, EMBASE, Web of Science, Science Direct, and Scopus for cohort studies assessing the association between HZ vaccination and dementia risk up to 20th January 2025. Hazard ratios (HRs) with 95% confidence intervals (CIs) were pooled adopting a random-effect model. Results Four eligible studies were included in the systematic review and five retrospective cohort studies in the meta-analysis. Among 14,493,383 dementia-free participants at baseline, 427,309 dementia cases occurred during 36-95 months of follow-up. All studies were of high quality. Pooled analysis of adjusted HRs indicated that HZ vaccination could reduce dementia risk by 29% (HR = 0.71, 95% CI: 0.66-0.76, I2 = 97.15%). Subgroup analyses revealed heterogeneity linked to definitions of dementia, exposure measurements, vaccination doses, deprivation index, and region. The results were stable in the sensitivity analyses, and no publication bias was found. Conclusions HZ vaccination was notably related to a reduced risk of dementia. More mechanistic studies and epidemiological studies are warranted.