The Shingles Vaccine and Dementia: What the Evidence Shows

TL;DR: Several large, unusually rigorous studies have found that people who get the shingles vaccine go on to develop dementia at a lower rate. The strongest, a natural experiment in Wales that used a birthday-based eligibility cutoff to mimic a randomized trial, found roughly a 20% lower rate of new dementia diagnoses over 7 years among those eligible for the vaccine. Studies of the newer Shingrix vaccine, and an independent replication in Australia, point the same direction, and the effect appears stronger in women. The leading theory is that preventing reactivation of the chickenpox virus, which causes shingles, reduces inflammation and damage in the brain. Important caveat: this is an association rather than proven cause and effect, and the first randomized trials designed to test it are only now getting underway. The reasonable move is to get the vaccine for the reason it is already recommended, to prevent shingles, and regard the possible dementia benefit as a bonus.

What does the shingles vaccine have to do with dementia?

At first the connection sounds odd: why would a vaccine against a painful skin rash affect the brain? The thread is the virus behind shingles. Shingles is caused by the varicella-zoster virus, the same one that causes chickenpox in childhood. After chickenpox, the virus does not leave; it goes dormant in your nerves and can reactivate decades later as shingles, most often when the immune system weakens with age. There has long been a suspicion that viruses which reactivate in the nervous system might contribute to the brain inflammation seen in dementia. If that is true, then a vaccine that stops the virus from reactivating might also spare the brain some damage.

For years this was a hypothesis with thin support. What changed is a series of large studies, several using clever designs that get closer to proving cause and effect than the usual observational research, all pointing in the same direction.

What did the Welsh natural experiment find?

The standout study came out of Wales in 2025.¹ When Wales rolled out the shingles vaccine, it set eligibility by exact birth date: people born on or after September 2, 1933 were offered the vaccine, and those born even a day earlier were not. That arbitrary cutoff created something close to a coin flip. The two groups, one just eligible and one just not, were otherwise nearly identical in age and health, so any later difference in dementia could be credited to the vaccine rather than to the kind of person who seeks it out.

That last point is what makes this study so valued. The usual weakness of vaccine research is that health-conscious people are both more likely to get vaccinated and less likely to develop dementia for unrelated reasons, which can create a false appearance of benefit. The birthday cutoff sidesteps that problem. And the result was striking: being eligible for the vaccine was associated with about a 20% lower rate of new dementia diagnoses, roughly a 3.5 percentage-point drop, over the following 7 years. The protection was concentrated in women, for reasons that are not settled but may involve their stronger immune response to vaccines.

Does the newer vaccine show the same thing?

This matters, because the vaccine used in Wales was the older, live version, called Zostavax, which the United States has largely retired. The vaccine people get today is Shingrix, a newer, more effective, non-live vaccine. So the natural question is whether Shingrix shows the same brain benefit.

The evidence so far says yes, though it is a step less airtight. A large study using United States health records took advantage of the near-overnight switch from the old vaccine to Shingrix around 2017, comparing people who got one versus the other.² Those who received Shingrix lived longer without a dementia diagnosis, gaining on the order of 17% more dementia-free time over 6 years, again with a larger effect in women. Meanwhile, an independent study in Australia repeated the Welsh birthday-cutoff design with the live vaccine and found a similar reduction in dementia over about 7 years, and further work has extended the pattern to earlier memory problems and even to slower decline in people who already have dementia.³⁴

No single one of these is a randomized trial, but their convergence is the point. Different countries, different vaccines, different study designs, and the arrow keeps pointing the same way.

Why might a shingles vaccine protect the brain?

Nobody knows for certain, and the theories are best held loosely. Three main ideas are on the table.

The leading one is the simplest: the vaccine prevents the chickenpox virus from reactivating, and each reactivation, even a silent one without a visible rash, can inflame blood vessels and nerve tissue in ways that, repeated over years, may nudge the brain toward dementia. Stop the reactivations, and you spare the brain that low-grade injury. A separate large study linking shingles episodes themselves to higher later dementia risk supports this idea.

A second theory points to the vaccine's broader effect on the immune system. Shingrix contains an ingredient called an adjuvant that revs up the immune response, and some researchers suspect this general immune tuning, sometimes called trained immunity, could protect the brain on its own. There is a catch, though: the older live vaccine has no such adjuvant, yet it shows the same benefit, so the adjuvant cannot be the whole story. That points back toward reduced viral reactivation as the shared explanation, with any adjuvant effect as a possible extra.

The third idea is a general version of the first: that lowering the body's overall burden of reactivating viruses and chronic inflammation is good for the aging brain in ways we are still mapping. For now these remain hypotheses, and untangling them is part of why randomized trials are needed.

Should you get the shingles vaccine for your brain?

Here is the bottom line. The evidence that the shingles vaccine lowers dementia risk is strong for observational research, unusually so, and it is convergent across many studies. But it is not yet proof. None of these studies is a conventional randomized trial with dementia as the planned endpoint, and association can still mislead even the best-designed observational work. The first randomized trials built to answer the question, in Denmark and Finland, are only now enrolling, and their results are years away.

So the guidance is measured. If you are 50 or older, you are already recommended to get the shingles vaccine, Shingrix, in two doses, to prevent shingles and its miserable complications, above all the lasting nerve pain that can follow. That recommendation stands on its own, strongly, regardless of the brain question. The possible dementia benefit is a reason to feel good about a vaccine you should get anyway, rather than a proven treatment to prevent dementia. If you have been putting the vaccine off, this is one more nudge to get it done. If you are hoping for a guaranteed way to prevent dementia, this is not yet that, and no one should present it as one.

A note on who and when: the strongest data come from older adults in their seventies and eighties, and the effect may not translate directly to a 50-year-old getting the vaccine today. That is not a reason to wait, since the shingles protection is worth having, but it is a reason to keep expectations grounded about the brain part specifically.

Guidance from the Clinic

"I find this one of the most encouraging stories in prevention right now, and also one where I have to police my own enthusiasm. When a patient asks me about the shingles vaccine and dementia, I tell them the truth in two parts. First, get the vaccine, without question, because it prevents shingles and the awful nerve pain that can trail it for months, and that alone earns it a place on your list at 50. Second, the dementia data are exciting, some of the best we have from studies that are not full randomized trials, and they all lean the same way, but they are not proof, and I will not promise you a vaccine will keep your memory intact. What I love about this is that it costs you nothing extra: you were going to get the vaccine anyway, and you may be protecting your brain as a bonus. That is the kind of low-risk, potential-high-reward move I build prevention around."

Related at Fishtown Medicine

• Cognitive Health and Dementia Prevention - the fuller picture of protecting your brain
• The New Alzheimer's Drugs (Leqembi, Kisunla) - the first disease-modifying treatments, once the disease has begun
• Hearing Loss and Dementia Prevention - another modifiable dementia-risk lever
• Chronic Inflammation and Aging - the inflammatory link this vaccine may act on
• Family History and a Prevention Plan - building prevention around your inherited risk
• The Four Horsemen - where dementia fits the longevity picture

Scientific References

1. Eyting M, Xie M, Michalik F, et al. "A natural experiment on the effect of herpes zoster vaccination on dementia." Nature. 2025;641(8062):438-446.
2. Taquet M, Dercon Q, Harrison PJ, et al. "The recombinant shingles vaccine is associated with lower risk of dementia." Nature Medicine. 2024;30:2777-2781.
3. Pomirchy M, Bommer C, Pradella F, et al. "Herpes Zoster Vaccination and Dementia Occurrence." JAMA. 2025.
4. Xie M, Eyting M, Bommer C, et al. "The effect of shingles vaccination at different stages of the dementia disease course." Cell. 2025.