Why is this relationship being investigated?
The varicella-zoster virus remains latent in nerve ganglia throughout life and can reactivate with age. The hypothesis that neuroinflammation, viral reactivation, and immune aging may contribute to the biology of dementia has been investigated for a long time. The potential effect of the vaccine may be through reducing viral reactivation, modulating the immune system, or a combination of both.
The Wales natural experiment
A 2025 Nature study utilized the Wales program, where eligibility for the shingles vaccine was determined by an exact date of birth. The fact that individuals immediately on either side of the threshold date were very similar except for age created a strong natural experiment that reduced the classic “those who get vaccinated are already healthier” bias. In the vaccine-eligible group, a reduction in dementia diagnoses was observed in subsequent years.
What did the Canadian data add?
A 2026 Lancet Neurology study evaluated similar age eligibility thresholds in Ontario. There were 464,637 individuals in the dataset; 232,124 individuals were included in the Ontario analysis. Over a five-and-a-half-year follow-up, being eligible for the vaccination program was reported to be associated with an approximately 2.0 percentage point absolute reduction in new dementia diagnoses. Similar results were obtained across two different eligibility thresholds.
Can we expect the same result with Shingrix?
A significant portion of the initial natural experiments comes from the live-attenuated Zostavax era. Today, recombinant Shingrix is used in many countries. Observational studies reporting a lower incidence of dementia are also available for the recombinant vaccine; however, the vaccine types, adjuvants, and study designs differ from one another.
Is it accurate to say “It reduces dementia by 20%”?
Some media reports use expressions of an approximately 20% relative risk reduction. This figure varies depending on the study design and outcome. The absolute risk difference may be smaller. In the Canadian natural experiment, the notable finding is an absolute difference of approximately 2 percentage points over 5.5 years. Therefore, it is not accurate to generalize a single relative percentage to all research.
Is it proven to prevent Alzheimer’s disease?
No. Studies mostly examine all-cause dementia diagnoses. The mechanism is not definitive, and large randomized vaccination trials with dementia endpoints have not yet been completed.
Clinical approach
The shingles vaccine should be considered in individuals appropriate for age and risk group to protect against herpes zoster and complications such as postherpetic neuralgia. A potential neuroprotective effect is an additional area of research; it should not be presented to the patient as an “Alzheimer’s vaccine.”
Limitations of the evidence
Although natural experiments are strong in terms of causality, they are not randomization. Factors such as coding errors in dementia diagnoses, vaccine access, and long-term health behaviors cannot be completely ruled out. The direct transferability of results between vaccine types is also uncertain.
References
- Eyting M, et al. A natural experiment on the effect of herpes zoster vaccination on dementia. Nature. 2025;641:438–446. DOI: 10.1038/s41586-025-08800-x.
- Pomirchy M, et al. Herpes zoster vaccination and incident dementia in Canada: an analysis of natural experiments. Lancet Neurol. 2026;25:170–180. DOI: 10.1016/S1474-4422(25)00455-7. PMID: 41579903.
- The Guardian, October 11, 2026: media review on shingles vaccine and dementia research.
Related readings: Healthy Aging and Biological Age
Last medical review: October 17, 2026
