Which is only relevant if you actually find an infectious agent doing something in the right place, which so far we have not.
The vaccine prevention connection for example AFAIK is just pure statistics: you get the shingles vaccine, your population level Alzheimer's risk drops but we have no direct evidence of why this should be.
Its entirely possible we later find it has no effect and it's a population level quirk of people who were likely to get a shingles vaccine until that research - conversely the cost of just getting one is incredibly low (hence why I did, in relation to that exact data).
