More Evidence for Vaccination to Reduce Alzheimer's Disease Risk

There is good evidence for the various forms of later life vaccination, such as for herpes zoster or influenza, to reduce the risk of later suffering Alzheimer's disease. One possibility is that people who take the time to obtain a vaccine tend to take better care of their health across the board. Another possibility is that vaccination produces a trained immunity effect that dampens age-related inflammation for a sustained period of time. It may also be the case that suffering from influenza, pneumonia, or similar infectious diseases causes sufficient additional inflammation to move the odds on suffering later neurodegenerative disease, and this is a large enough effect to show up in sizable study populations with an increased infection risk and severity for the unvaccinated. Regardless, this is an interesting area of research that is clearly connected to the growing interest in the role of chronic inflammation in the development of age-related neurodegenerative conditions.

Accumulating evidence suggests that adult vaccinations can reduce the risk of developing Alzheimer's disease (AD) and Alzheimer's disease related dementias. To compare the risk for developing AD between adults with and without prior vaccination against tetanus and diphtheria, with or without pertussis (Tdap/Td); herpes zoster (HZ); or pneumococcus, a retrospective cohort study was performed. Included patients were free of dementia during a 2-year look-back period and were ≥65 years old by the start of the 8-year follow-up period. We compared two similar cohorts identified using propensity score matching (PSM), one vaccinated and another unvaccinated, with Tdap/Td, HZ, or pneumococcal vaccines. We calculated the relative risk and absolute risk reduction for developing AD.

For the Tdap/Td vaccine, 7.2% (n = 8,370) vaccinated patients and 10.2% (n = 11,857) unvaccinated patients developed AD during follow-up; the relative risk was 0.70 and absolute risk reduction was 0.03. For the HZ vaccine, 8.1% (n = 16,106) vaccinated patients and 10.7% (n = 21,273) unvaccinated patients developed AD during follow-up; the relative risk was 0.75 and absolute risk reduction was 0.02. For the pneumococcal vaccine, 7.92% (n = 20,583) vaccinated patients and 10.9% (n = 28,558) unvaccinated patients developed AD during follow-up; the relative risk was 0.73 and absolute risk reduction was 0.02. Thus several vaccinations, including Tdap/Td, HZ, and pneumococcal, are associated with a reduced risk for developing AD.