Routine Vaccinations and Alzheimer Disease Risk
In this video, Paul Schulz, MD, discusses the results of his team's latest study examining the impact of various routine vaccinations on Alzheimer disease risk in individuals 65 years of age or older. This video is part one in a three-part series.
Additional resource:
- Harris K, Ling Y, Bukhbinder AS, et al. The impact of routine vaccinations on Alzheimer's disease risk in persons 65 years and older: a claims-based cohort study using propensity score matching. J Alzheimer's Dis. 2023;95(2):703-718. doi:103233/JAD-221231.
Watch part two of this three-part series here.
Watch part three of this three-part series here.
TRANSCRIPTION:
Paul Schulz, MD: My name is Dr Paul Schultz, and I'm a professor of neurology at the University of Texas Health Science Center in Houston.
C360: This latest study comes just a year after your team found that individuals aged 65 years or older with at least once vaccination against influenza were 40% less likely to develop Alzheimer disease (AD) than those who were unvaccinated. Could you discuss how the results of this study prompted this recent analysis?
Dr Schulz: That's a really good question, and lemme tell you why. So for years we've known that people who get infections of any sort who have Alzheimer's get a lot worse, and sometimes it even triggers the initial presentation of Alzheimer's. So I've also thought in the back of my mind for decades, that when people get vaccinations, they get inflammation associated with that. And of course, it's really good in the sense that it prevents you from getting something deadly like the flu, but God forbid it would make them worse in terms of their Alzheimer's because it's inflammation just like the flu and other infections that we know make Alzheimer's worse. So I was honestly expecting to find that the vaccines might have a small positive effect on bringing out Alzheimer's. I was absolutely delighted to find out that after all these years of giving people the flu vaccine that we were having, if anything, a positive effect.
And so this most recent study looking at other vaccines was actually engendered from that because once we found that the flu vaccine reduced the risk of Alzheimer's pretty dramatically, we started asking questions like, well, is it specific to the flu vaccine? It turns out that when you get vaccinated, you actually get the outer coating of a virus - that's dead, it doesn't have the stuff in the middle that's infectious - and it turns out that the outer coating of the influenza virus looks a lot like beta amyloid plaques in the brain that are causing the Alzheimer's disease. So one hypothesis was that when we give people a flu vaccine, maybe it happens to look like the beta amyloid, so we're actually vaccinating against the amyloid and getting rid of it.
We thought, well, that's possible. If we tested other vaccines and they didn't have the same effect, then maybe that was true. But if we tested other ones and had a positive effect on preventing Alzheimer's then we would know that it wasn't specific to the flu at all. It's a property of whatever vaccines do to our body. The other thing that as an investigator is always in the back of your mind, if you look around and you find the flu vaccine prevents Alzheimer's, you always wonder is there something in the data that you're not aware of that might make it spurious. And so looking at other vaccines also came about because if we found several that were positive, then it would kind of give us more confidence that vaccines are working. And it wasn't just that we happened to look at a particular population. So yes, good question. There was a lot of reasons why after the first finding we made was published, we went on to look at other vaccines to see if the effect was specific and in the other direction to kind of corroborate the idea that vaccines might actually work. And then that's what we found. The other ones worked and that corroborates our initial finding.
C360: Your study noted that the risk of Alzheimer disease varied greatly among the two types of vaccines for herpes zoster but was similar among the two types of pneumococcal vaccines. Is this a result that surprised you, or did you anticipate this?
Dr Schulz: With zoster particularly, this probably isn't common knowledge, especially if you're young and you don't need to get the vaccine. But there was a form of the vaccine that was a little weaker and not so effective, but we all used to get it because it was what we had. And that changed to Shingrix maybe 5, 7 years ago, which is a lot more effective at preventing shingles. And for those of us who were born before we had the chickenpox vaccination - I had the actual chickenpox, but then my brother and sister who were younger than me got the vaccination. Anyway. Once you've had chickenpox, that virus hangs out in your body forever. So you want the most efficacious vaccine to prevent it. But to answer your question, then the new vaccine is very different than the old one. And so it's very possible they would have different effects.
The pneumococcus one is interesting. There's a lot of different forms of pneumococcus and I didn't know if they would be different or whatever... Around every plaque in the brain in Alzheimer's there's activated inflammation cells. And it's their activation that's actually thought to lead to brain cell death in Alzheimer's. So the amyloid by itself is kind of inert, but once the inflammatory cells recognize it as being foreign they start releasing things to kill it. But they can't because it's chemically inert and they release these factors for 10 to 20 years before we see someone. And I'm saying this to kind of get the point across that in theory, things that increase or decrease the activity of the inflammatory cells in the brain could have a big impact on Alzheimer's. And I'm thinking that the several vaccines that are positive, may be positive because they're actually having an inhibitory effect on the brain inflammatory cells. So when I get the vaccine here, the peripheral, we call it peripheral inflammatory cells, the white blood cells, react to that and protect me from whatever virus it is that we're injecting against. But those factors may go through the body and turn off, accidentally, the brain inflammatory cells. As I mentioned, it could have gone the other way, that it could have turned them on too and made people worse when they got vaccines in terms of Alzheimer's. But it seems to be the opposite of that.
Thank you so much for having me. It's a real pleasure.