TLDR
Among comparable older adults, getting the older shingles shot was followed by about 20% fewer new dementia diagnoses over seven years. The benefit may come from preventing virus activity, changing immune responses, or both.
Summary
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1 Study Aim
The authors aimed to test whether the live-attenuated zoster vaccine (a vaccine containing a weakened virus) prevents or delays new dementia diagnoses. They sought stronger evidence than ordinary comparisons between vaccinated and unvaccinated people by using Wales’s birth-date eligibility rule. The study also explored whether the effect differed by sex and how vaccination might influence dementia. The study tested whether the older shingles shot could reduce new memory-loss diagnoses.
2 Study Design
The study used a natural experiment (a real-world policy rule that creates nearly comparable groups). In Wales, people born before 2 September 1933 were never eligible, while those born afterward were eligible. Researchers applied a regression discontinuity design (comparing outcomes immediately around a cutoff) to electronic health records from the Secure Anonymised Information Linkage (SAIL) Databank. The main cohort included 282,541 adults without dementia, followed for seven years. Two-stage least-squares analysis estimated effects of actually receiving Zostavax. The researchers checked results using other outcomes, methods, and death certificates from England and Wales. The researchers compared people born just before and after the vaccination cutoff, then tracked their health.
3 Findings
The research found that vaccine eligibility increased vaccination from 0.01% to 47.2%. Actually receiving Zostavax reduced new dementia diagnoses by 3.5 percentage points over seven years, a 20.0% relative reduction. The 95% confidence interval (a range showing statistical uncertainty) was 6.5% to 33.4%. Effects were stronger among women. Vaccination also reduced shingles, while other major health outcomes and preventive behaviors showed no comparable change. Death-certificate analyses supported the dementia finding, as did a difference-in-differences instrumental-variable analysis (a second method using policy timing to estimate effects). Exploratory analyses suggested roles for reduced varicella-zoster virus (VZV) reactivation and broader immune changes. The authors recommend randomized trials and mechanistic research. Results apply to Zostavax, not Shingrix, and mainly to people near age 80. The older shingles vaccine appeared to delay or prevent some dementia cases, but more testing is needed before treating this as certain.