For years, scientists have known that there’s a weird link between shingles and dementia.

On the surface, a blistery rash doesn’t seem related at all to brain deterioration… aside from how shingles hurts so bad that it can make you feel like you’re losing your mind. But as unrelated as the two may sound, we have a lot of data supporting  a correlation between them.

Now, correlations don’t mean that shingles necessarily causes dementia. Or that /not/ getting shingles prevents dementia. And it’s not the kind of thing we could really run an experiment to test.

Until now. Several studies published in  2025 used natural experiments to demonstrate this link more  clearly than ever before. And they established something even more exciting: the shingles vaccine may  actually help prevent dementia. [♪INTRO] If you’ve ever had shingles, you’re more likely to eventually experience dementia.

According to a 2020 study of insurance claims, people who had shingles at any point in their life were nearly 20 percent more likely to develop dementia compared with  people who had never had it. See, shingles is caused by  the herpes zoster virus. Yes, a herpes virus is at the root  of those painful torso blisters.

And, yes, it’s related to those herpes viruses you know for the cold sores and  other sores they produce. But it’s not the same virus. Herpes viruses have been suspected for years to provoke the hallmarks of dementia, like inflammation in the brain  and amyloid beta plaques.

At first, the latter appears to be a good thing. The amyloid beta plaques  fight off your herpes virus by attaching to proteins that stick  out from the virus and entombing it. But the long term accumulation of these plaques is a sign you have a chronic problem.

One research team analyzed  the brains of people who had been diagnosed with Alzheimer’s  disease and subsequently died. They found that the majority  of herpes virus in the brain was concentrated  inside amyloid beta plaques. And 90% of the plaques they  found had herpes virus in them.

So the virus isn’t found  much outside of the plaques, and the plaques aren’t found much  without virus inside of them. Which means herpes viruses  and hallmarks of dementia are pretty specifically in  the same places in your brain. And if you’re wondering which one’s the chicken and which one’s the egg, the virus is the chicken.

Or whichever you think comes first. The virus comes first. A study found that the virus  basically hyperactivates the enzymes that make amyloid beta plaques.

So it pretty much commissions  the mason that builds its tomb. And the fact that the virus  and the plaques stick together made some researchers think  that we could use the stuff that prevents the shingles  virus to treat dementia, too. This idea is not new, but  it’s been really hard to test.

Historically, results are always  clouded by the fact that people who get vaccinated are generally  also practicing other healthy habits. It was really hard to find two  groups of people who were pretty much the same except that one group got the shingles vaccine and the other didn’t… Until 2013! Now I know what you’re thinking.  Deboki, 2013 is not recent.

Whatever happened that year shouldn’t be ground breaking news in 2026. But! Researchers needed to  collect data for years to see how the shingles vaccine  might affect people over time.

Especially because dementia isn’t the kind of thing that kicks in over night. So stay with me. It’s 2013, and we’re in Wales.

A new shingles vaccine just dropped. If you’re 80 years or older,  you’ve literally missed your shot. The shingles vaccine was  only made available to people under 80 on September 2nd when  they started rolling it out.

Bam! We’ve got a natural experiment. Without having to design or recruit for a study, researchers just had to get  permission to look through the health records of people in  Wales to see how rates of dementia compared among people who had been 79 and 364 days old versus the 80 year olds.

Okay, that kind of comparison  was a bit too good to be true. They actually pooled data  from two 8-year age ranges. So in the group that had access to the vaccine, they had people who were 71 to 79 years old.

And in the unvaccinated group,  they had 80 to 88 year olds. And they specifically compared  the records of only people who had not been diagnosed with dementia  at the start of the program. That way, they could see who developed dementia and who didn’t in relation to  having access to the vaccine.

But before I tell you about the results, all research needs funding, including ours. So here’s a quick ad from one of our sponsors. Thank you to our Presidents of  Science, Binorthedrunkdwarf, Harry Plumley, Raz Tirosh, and Charlie Stanley, for supporting this SciShow video!

They make it possible for you to watch these videos and learn so much stuff for free. These folks are helping pay my  salary so that I, and our whole team, can devote the time it takes  to put together multiple high quality, fact-based, and beautifully  designed videos every week. Our Presidents of Science  work along with other patrons on Patreon and you, our  viewers who comment on videos and share them with people you  know, all so that knowledge and curiosity can reach as  far and wide as possible.

If you’d like to join our  Presidents of Science in financially supporting it all, you can do  that at patreon.com/SciShow. In 2020, after collecting data for seven years, they found 20% less dementia among people in the vaccinated group than  their unvaccinated peers. That’s a really big effect  from a single vaccination.

And it was the first time that link had been demonstrated that thoroughly! But there are a couple of caveats to the data that might bring things back to Earth a bit. Remember, they weren’t comparing a giant sample of people who were one day apart in age.

They were comparing people in  their 70s with people in their 80s. And all sorts of health stuff can  look different between those groups. Also, less than half of the people in the eligible group actually did get the shingles vaccine.

Which means the raw numbers for the study were lower than they could have been, and the mindblowing 20% stat  only came from adjusting the data to what it would have looked like  with a higher vaccination rate. They’re basically saying,  “Imagine what these numbers would look like if everyone  who could get the vaccine did!” That said, it’s still a remarkable outcome. So remarkable that the research team needed to find another population to  make sure it wasn’t a fluke.

And conveniently, other countries have followed Wales with similar shingles vaccine roll-outs. So they have been able to  replicate their findings. They conducted pretty much the  same analysis of Australia’s data and found that the shingles vaccine was associated with a reduction in their dementia rates, too.

This is really exciting for people  who don’t want to develop dementia, which is most of us. But an even more recent study from  the same research group is giving hope to those who might already be  in the early stages of dementia. This study concluded that  the shingles-dementia link is not just about prevention.  It can even slow progression!

By analysing the Wales data in new ways, the researchers found even more cool effects of shingles vaccines on dementia. Like reduced dementia-related deaths among the group that got the shingles vaccine! This time, the researchers  compared the thousands of people who got the shingles vaccine  after their dementia diagnosis with those who had dementia  but didn't get the vaccine.

And among the vaccinated  group, there were 8.5% fewer dementia-related deaths over the next nine years. And those effects aren’t specific  to a certain kind of dementia. Or to a certain stage of the disease.

The shingles vaccine seems  to reduce dementia-related hospital admissions, deaths, and other bad outcomes across the entire disease course. So the shingles vaccine seems  to be protective against developing dementia and against its progression. We just don’t know exactly why.

But, as always, scientists have some ideas. The first possibility is that  this is all a bunch of hullabaloo. You can get the shingles vaccine and still develop dementia at the same rate.

But if you don’t go to the  doctor to treat shingles, then your dementia won’t be caught  and in your medical records. I have to bring this up first to assure you that researchers have thought about this possibility. But they don’t think that this would result in the relatively large difference in dementia diagnoses they observed between the two groups.

Especially because they knew that these people were seeing their primary  care physicians regularly. Another explanation is that  the act of getting a vaccine, regardless of whether it was  for shingles or something else, could have triggered an immune response that protected against dementia. This would mean that the shingles-dementia link isn’t as specific as we think.

We can’t rule that out based  on the data we have today. But to some researchers, the evidence for the next explanation is most convincing. It’s the idea that specifically keeping the shingles virus quiet prevents dementia.

And it’s supported not just by  the evidence I’ve shared so far, but a giant years-long analysis  from yet another country’s data. In the United States, researchers  analyzed the health records of more than 100 million people  who were at least 50 years old. And they found the same  shingles-dementia relationship that the data from Wales  and Australia highlighted.

But this time, they also analyzed  the data to see if the same relationship could be observed for  the pneumococcal polysaccharide vaccine that fights pneumonia,  meningitis, and other infections. If that vaccine also prevented dementia, then we’d have support for the second explanation. It might just be an immune booster and nothing special about the shingles vaccine.

But that’s not what they found. People who got the shingles vaccine had a 33% reduced risk of developing dementia compared to people who got the pneumonia vaccine. So it does look like the weird  association between shingles and dementia is a specific  relationship between those diagnoses.

Who knows? Maybe the next study will start seriously looking at the shingles vaccine as a dementia treatment. And considering how affordable and  available the shingles vaccine is, it could be a way more  effective dementia prevention strategy than what we’ve been working with.

So vaccinations could be even more life saving than we thought they were! And we already thought they were one of the most life-saving technologies  humanity has to offer! Is there anything they can’t do? [♪OUTRO]