Can varicella-zoster vaccine provide protection against dementia?

The findings from a study published in the Cold Spring Harbor Laboratory strongly suggest that the varicella-zoster virus, which causes both shingles and chickenpox, may play a crucial role in the etiology of dementia. 

To investigate causal evidence on the connection between herpesviruses and dementia, Markus Eyting and team in Wales capitalized on a unique opportunity provided by the herpes zoster vaccine, also known as Zostavax, which is administered for shingles prevention. In Wales, eligibility for the vaccine was determined based on an individual's precise date of birth. Those born before September 2, 1933, were ineligible for the vaccine for life, while those born on or after this date were eligible. Leveraging comprehensive nationwide data on vaccinations, medical encounters, death records, and patients' dates of birth, researchers conducted an analysis to examine the impact of the vaccine on dementia occurrence.

The study revealed a striking difference in the percentage of adults receiving the herpes zoster vaccine based on their eligibility. Among patients who were just one week too old to be eligible, a mere 0.01% received the vaccine. In contrast, 47.2% of those born just one week later, making them eligible, received the vaccine. 

Utilizing this unique natural randomization, the study established a robust causal effect estimation. Initially, the researchers replicated the vaccine's known effect of reducing the incidence of shingles. Furthermore, they found that receiving the herpes zoster vaccine reduced the likelihood of a new dementia diagnosis by 3.5 percentage points (95% CI: 0.6 – 7.1, p=0.019) over a seven-year follow-up period. This reduction corresponded to a significant relative decrease of 19.9% in the occurrence of dementia. Notably, the vaccine did not exhibit any significant effects on other common causes of morbidity and mortality.

Exploratory analyses also indicated that the protective effects of the vaccine against dementia were more pronounced among women compared to men. While the study provides important insights, further randomized trials are required to determine the optimal population groups and timing for administering the herpes zoster vaccine to prevent or delay dementia. Additionally, future investigations should employ more precise measures of cognition to quantify the magnitude of the causal effect.

Source:

Eyting, M., Xie, M., Heß, S., Heß, S., & Geldsetzer, P. (2023). Causal evidence that herpes zoster vaccination prevents a proportion of dementia cases. Cold Spring Harbor Laboratory. https://doi.org/10.1101/2023.05.23.23290253