Older adults eligible for the herpes zoster vaccine experienced a 20% lower risk of developing dementia over 7 years, according to a recent study.
Published in Nature, researchers used a regression discontinuity design to evaluate dementia incidence among older adults in Wales based on eligibility for vaccination determined by a date-of-birth cutoff.
The analysis included 282,541 adults born between September 1, 1925, and September 1, 1942, without a prior diagnosis of dementia before the vaccine rollout on September 1, 2013. The primary outcome was any new dementia diagnosis—defined using primary care, hospital, and mortality records—within a 7-year follow-up period.
Researchers led by Markus Eyting, from the Department of Medicine, Stanford University, California, and colleagues, used local linear regression with a triangular kernel and a mean squared error–optimal bandwidth to estimate causal effects at the date-of-birth threshold of September 2, 1933, which determined eligibility for the national zoster vaccination program.
During follow-up, 35,307 participants were newly diagnosed with dementia. Eligibility for the herpes zoster vaccine was associated with a 1.3% absolute reduction in dementia incidence, corresponding to an 8.5% relative reduction. After adjusting for incomplete vaccine uptake using instrumental variable analysis, receipt of the vaccine was associated with a 3.5% absolute reduction in dementia diagnoses, equating to a 20% relative risk reduction.
"Our substantial effect sizes, combined with the relatively low cost of the zoster vaccine, imply that, if these findings are truly causal, the zoster vaccine will be both far more effective as well as cost-effective in preventing or delaying dementia than existing pharmaceutical interventions," noted Eyting and colleagues.
The findings were consistent across sensitivity analyses, including varying the bandwidth around the cutoff, applying different grace periods, and using alternative dementia definitions such as the initiation of dementia-specific pharmacotherapy. No discontinuities were observed at the eligibility threshold for unrelated health behaviors, health care use, or demographic characteristics, supporting the validity of the design and minimizing the likelihood of residual confounding.
The researchers noted that further investigation is warranted to clarify underlying biological mechanisms and assess whether the findings can be replicated in other populations.
The researchers reported no conflicts of interest.
