Longevity Briefs: Many Vaccines Seem To Protect Against Alzheimer’s

Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

Why is this research important: There’s pretty good evidence that people who are vaccinated against various diseases, perhaps most notably influenza, are also less likely to get Alzheimer’s disease. But why? People who are better educated are more likely to get vaccinated, and we know that education is associated with reduced Alzheimer’s risk. People who choose to get vaccinated are also more likely to care about their health, and therefore to follow other healthy practices that might reduce their risk.

Yet even when such factors are accounted for, there still seems to be a relationship between vaccination and Alzheimer’s prevention. This could have something to do with inflammation, a process that we are increasingly realising is an important driver of neurodegenerative disease. Vaccination allows the immune system to swiftly eliminate a pathogen with tailor-made immune cells, which reduces the reliance on non-specific inflammation to keep infection at bay. Perhaps this results in reduced inflammation over long periods of time – enough to reduce the risk of Alzheimer’s disease in old age.

What did the researchers do: This study looked at data from over 1.6 million people, mostly from the United States. Vaccination and Alzheimer’s incidence was tracked over 8 years and participants were aged 65 or over and free of dementia at the start of this period. The researchers looked at participants who received vaccinations against tetanus and diphtheria with or without pertussis (Tdap/Td), herpes zoster (HZ) or pneumococcus. They looked at how many of these people developed Alzheimer’s disease in comparison to those who were unvaccinated. In an attempt to control for confounding factors, researchers used propensity score matching, a technique in which a matching control group is constructed that closely matches the characteristics of the experimental group (apart from the experimental variable of course – in this case vaccination status).

Key takeaway(s) from this research: Vaccinated participants had a significantly reduced risk of Alzheimer’s disease during the follow-up period. In comparison to the matched unvaccinated participants, risk of Alzheimer’s was 30% lower for Tdap/Td, 25% lower for HZ, and 27% lower for pneumococcal vaccine. Researchers also found evidence that the specific type of vaccine (such as live-attenuated or recombinant) influenced the risk of developing Alzheimer’s disease differently.

This was a retrospective study, meaning that researchers looked back at vaccination data that already existed, rather than selecting vaccinated and unvaccinated people and following them up to see what happened. Performing a retrospective study means that less information is available to control for confounding factors and that there is more susceptibility to various forms of bias. For example, the data used came exclusively from individuals with both medical and prescription coverage, which limits the generalisability of the results.

That being said, this research aligns with previous studies looking at the same vaccines. It suggests that there are even more good reasons to get vaccinated, even in old age when vaccines are generally less effective.