Getting vaccinated against shingles — a painful and debilitating condition that can flare up years after infection from varicella zoster — not only lowers the risk of infection, but may also offer some protection against dementia, a provocative new study suggests.
The new research, published Wednesday in Nature, analyzed data from more than 280,000 older adults in Wales and found that people who received the original shingles live virus vaccine were 20% less likely to develop dementia of any type than those who were not vaccinated.
Previous research has found an association between the Shingrix shingles vaccine, which replaced the live virus version in 2020, and a lower risk of dementia, especially in women. But that link wasn't considered as strong because that study design couldn’t account for potential differences between those who were vaccinated and those who were not, such as the possibility that the vaccinated people might have been healthier overall. Shingrex, which targets a tiny bit of viral DNA, turned out to have a longer lasting effect than the original vaccine.
The new study was possible because of an unusual public health policy in Wales that provided a “natural experiment” to explore the potential impact of the vaccine on dementia risk. With the rollout of the vaccine in 2013 in Wales, shots were offered to people born on or after Sept. 2, 1933, but not those who were born before that date.
That allowed the German and Stanford University researchers to compare two groups of people with similar health characteristics who differed only by one week in age, making them essentially the same except that the vaccine was available to the younger population but not the older, said Dr. Pascal Geldsetzer, an assistant professor of medicine at Stanford University and senior author of the study.
What’s exciting about the study is that it’s essentially like a randomized controlled trial, considered the gold standard in research, he said.
The way the original vaccine was rolled out in Wales provided a unique opportunity, said Allison Aiello, a professor of epidemiology at the Columbia University Aging Center in New York City.
“It’s like having a control group compared to a treated group,” said Aiello, who was not associated with the new research. “What’s interesting is the finding of 20% protection. That is a pretty strong effect, which does fit with other research suggesting that herpes viruses might have an influence on dementia.”
Scientists don’t know exactly how the chickenpox virus raises the risk of dementia. It’s been shown that reactivation of the virus can lead to the accumulation of aberrant proteins associated with Alzheimer’s, for example, Geldsetzer said. It’s also possible that the virus might spark a reactivation of herpes simplex, which earlier research has linked to dementia.
Herpes viruses never completely go away, but instead lurk in the body until the immune system weakens. Aging leads to a natural weakening of the immune system that can allow the virus to resurface as shingles, a nasty side effect of chickenpox.
The age effect is why the shingles vaccine has been offered only to people age 50 and older in the U.S. It's given as two doses, two to six months apart.
Herpes viruses, including oral and genital herpes simplex, appear to have the ability to get into the central nervous system, experts said.
In fact, a 2024 study found that among 70-year-olds without dementia at the outset, older adults with a herpes simplex diagnosis were more than twice as likely as uninfected people to develop dementia over a 15-year follow-up.
Herpes simplex can wreak havoc if it passes through the blood-brain barrier. It can cause inflammation of both the meninges (meningitis) and the brain (encephalitis). Both can be fatal.
Bolstering the case for the shingles vaccine protecting against dementia were the findings from a study published in Nature Medicine in 2024 that analyzed medical records from more than 100,000 patients. That analysis suggested the newer shingles vaccine was associated with even better protection against dementia.
In that study, researchers also investigated whether two other vaccines — for influenza and tetanus, diphtheria and pertussis — had any impact on the risk for dementia. They did not.
The most important take-home message from the Stanford study is that getting vaccinated might lower the risk for dementia, said Dr. Aarati Didwania, a professor of medicine and medical education at Northwestern University’s Feinberg School of Medicine in Chicago.
Exactly how the vaccines might protect against dementia isn’t clear, Didwania said. “But it’s an intriguing question,” she added. “Is it by decreasing inflammation or preventing the virus from reactivating?”
There’s certainly a good reason for getting vaccinated, Didwania said.
“Shingles is a terrible, painful and debilitating condition that can lead to horrendous long-term pain,” she said.
There are limitations to the new study. While it indicates the benefit of the vaccine in a real-world setting, it's not the same as a randomized controlled trial, said Dr. William Schaffner, a professor of infectious diseases at the Vanderbilt University Medical Center in Nashville, Tennessee. But it wouldn't be ethical to randomly assign people to get the vaccine or not, he said.
“It’s provocative, interesting and exciting,” he said of the research.
It’s possible that the Food and Drug Administration could review research linking shingles vaccines to a lower risk of dementia and allow the drug company to add that indication to the label, Schaffner said.
Even if that doesn’t happen, doctors can use the study findings to convince patients to choose to be vaccinated.
“Clearly there are lots of people 50 and over who have not received the vaccine,” he said. “If you say there are some data that suggest the vaccine might prevent some cases of dementia, people might be persuaded.”
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