An annual flu shot seems to be protective not only against the flu but against Alzheimer’s disease–and possibly against the cognitive effects of CAA (Cerebral Amyloid Angiopathy). Here is a link to this research:
https://www.webmd.com/vaccines/news/20220630/flu-vaccine-older-minds-sharp-study

According to WebMD, “In a large study of vaccinated and unvaccinated adults ages 65 and older, those who received at least one influenza vaccine were less likely than unvaccinated peers to get Alzheimer’s over the course of 4 years.”

The research was based on nearly one million seniors vaccinated against the flu and another group of similar size that had not been vaccinated. Over 4 years, the risk of getting Alzheimer’s was 40% lower in the vaccinated group. This is an incredible difference, especially given than the results are based on a study of nearly 2 million people.

Moreover, it seems that past studies have shown a protective effect for many other vaccines. Therefore, it is even possible that Covid vaccines might be beneficial as well, although that would need to be studied.

According to Heather Snyder, PhD, with the Alzheimer’s Associtation, however, it is “too early to tell if getting flu vaccine, on its own, can reduce risk of Alzheimer’s…it is possible that people who are getting vaccinated also take better care of their health in other ways, and these things add up to lower risk of Alzheimer’s and other dementias…[or] that there are issues related to unequal access and/or vaccine hesitancy and how this may influence the study population and the research results.”