It looks like the shingles vaccine has positive effects that prevent dementia. (Well, that's in the title.)

This study was possible due to a "natural experiment" where one country gave people from a very specific birth date the vaccine (so people born right before and right after that date were very similar, except for the vaccine).

It's not clear why this is the case. It might be that the virus the vaccine supresses plays a role in dementia development, or it might be that the vaccine causes an immune response that has other indirect positive impacts.