I'm not skilled, but it feels like a validation for the virus theory of dementia

https://med.stanford.edu/news/all-news/2025/03/shingles-vacc...

"The remarkable findings, published April 2 in Nature, support an emerging theory that viruses that affect the nervous system can increase the risk of dementia. If further confirmed, the new findings suggest that a preventive intervention for dementia is already close at hand."

The highlights are a good start. (I’m a doctor, just a nerd who likes to read papers.)

My comments in brackets.

- Herpes zoster vaccination reduced dementia diagnosis in our prior natural experiments. [Previous work. I’m familiar with the Wales experiment where they had a sharp age cutoff for getting the vaccine in their national health system. Comparing those just below and just beyond the cutoff allows for analysis similar to a randomized controlled trial (aka ‘natural experiment’). The results showed a ~20% decrease in dementia due to vaccine, so the results were already pretty strong.]

- Here, we find a lower occurrence of MCI and dementia deaths among dementia patients [MCI = ‘mild cognitive impairment’. This is a more refined result than prior work, harder to see in the data than a clear dementia diagnosis.]

- Herpes zoster vaccination appears to act along the entire clinical course of dementia. [This is not surprising given the earlier results, but the demonstration is harder, and it may lead to recommendations for earlier HZ vaccination, IIRC currently at 50 or 55 in the US.]

- This study’s approach avoids the common confounding concerns of observational data [Basically they are improving their methods and getting stronger results, classic good science.]

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.

Shingles attacks your nervous system. Avoiding shingles prevents it from damaging your brain, so it isn’t surprising the vaccine reduces dementia.

There are multiple causes for dementia. If I read figure 2 right, the vaccine slightly reduces the chance of mild cognitive impairment, but cuts the chances of dying from dementia by about a third(!)

Also interesting: The vaccine helps at different phases of disease progression.

The simplest explanation is that dementia is due to cumulative damage, not a single event, and that getting shingles is a big hit.

The vaccine probably prevents dementia in the same way staying out of planes makes you invulnerable to parachute failures.

This is probably a key sentence: "...the effect of actually receiving the HZ vaccination was a 3.1 (95% CI: 1.0–6.2, p = 0.007) percentage point reduction in new diagnoses of MCI over 9 years."

MCI = mild cognitive impairment

What's interesting to me is that the effect doesn't appear to be specific to Alzheimer's--rather they see a reduction in all forms of dementia diagnosis.

I suspect the thinking is something along the lines of ... dementia is either caused or heavily influenced by inflammation. Reactivation of HZ virus causes neurological inflammation. So, HZ vaccination is gonna prevent some forms of inflammation and help you avoid dementia--a little bit.

FWIW, I'm trained as a molecular biologist and have a some knowledge of clinical trials, dementia, etc., but I am far from an expert on this.

Statistics show that in some populations there is less dementia among those who received the shingles vaccine than among those who didn't.