On September 1, 2013, Wales launched a shingles vaccine program where residents who were 79 on that date could receive the vaccine, and those who were 80 or older by that date were not eligible.

This, researchers explained, provided a randomized trial for examining a potential link between the shingles vaccine and dementia risk, providing findings for their April 2025 study.

“In medicine, what you need to prove that an intervention, like a medication or a vaccine, works is a randomized trial,” Pascal Geldsetzer, MD, PhD, assistant professor of medicine in the Division of Primary Care and Population Health at Stanford University, and senior author of this study, told Medical News Today.

“What’s so special about our study is that we take advantage of a very similar scenario to a randomized trial. We see in our data, that just a 1-week difference across this date-of-birth cutoff means that you go from essentially no one getting vaccinated to about half of the population getting vaccinated,” Geldsetzer added.

With this follow-up study, scientists decided to analyze the health records of study participants further by looking at the earliest signs of cognitive decline to late-stage dementia.

At the study’s conclusion, scientists found that study participants who received the shingles vaccine showed a lower probability of receiving a mild cognitive impairment diagnosis during the following nine years, compared to those who were not vaccinated.

Additionally, vaccinated participants were significantly less likely to die from dementia after receiving a diagnosis in the nine years following. This, researchers said, suggests the shingles vaccine may help slow the advancement of dementia.

“For the first time, we now have evidence that likely shows a cause-and-effect relationship between shingles vaccination and dementia prevention and treatment. We find these protective effects to be large in size — substantially larger than those of existing pharmacological tools for dementia.”

– Pascal Geldsetzer, MD, PhD

With studies showing a potential link between the shingles vaccine possibly preventing dementia or slowing its progression, the next question is how does this work?

Geldsetzer said there are broad mechanisms that could be at play here and they are not mutually exclusive.

“The first mechanism is specific to the chickenpox virus,” he explained. “There is a growing body of research showing that viruses that preferentially target your nervous system and hibernate in your nervous system for much of your life may be implicated in the development of dementia. One such virus of course is the chickenpox virus, which can cause shingles later in life.”

MNT also spoke with Zeeshan Khan, MD, chief of geriatrics at Hackensack Meridian Jersey Shore University Medical Center in New Jersey — who was not involved in this study — who said there are two primary theories as to why reducing shingles could also protect the brain.

“Neuroinflammation reduction — this is the leading theory,” Khan detailed.

He explained:

“The shingles virus, varicella-zoster, lies dormant in the nerve cells after a person has had chickenpox. When it reactivates, it causes not only a painful rash but also significant inflammation within the nervous system. It is this neuroinflammation that is thought to trigger or accelerate the processes that lead to dementia, such as the buildup of abnormal proteins in the brain. By preventing the virus from reactivating, the vaccine would prevent this inflammatory response, thereby protecting the brain from damage.”

“A second possibility is that the vaccine provides a broader, non-specific boost to the immune system,” Khan continued.

“This ‘revving up’ of the body’s defenses might make the immune system more effective at clearing out the abnormal proteins associated with Alzheimer’s disease or managing other age-related cellular damage in the brain. The fact that other vaccines have also been linked to a reduced dementia risk adds some support to this idea,” he added.

Khan told MNT that his first reaction on seeing the study’s findings was both excitement and cautious optimism.

“In geriatrics, we are often confronted with the profound impact of dementia not only in our patients but their loved ones as well,” he explained. “It suggests that a routine preventative measure we already recommend for shingles could have a powerful effect on brain health. Currently, we have so few effective interventions, and this presents a readily accessible option.”

“Further, to see that this study as a ‘natural experiment,’ took the steps to minimize many of the usual biases that we see in observational research makes the results even more compelling,” Khan added. “This study reinforces the importance of vaccination in our older adults as a whole.”

MNT also spoke with Raphael Wald, PsyD, a neuropsychologist with Marcus Neuroscience Institute, part of Baptist Health South Florida, about this research.

“This further confirms that the shingles vaccine decreases the risk of dementia,” Wald commented. “Because the study is so unique in design, it also provides evidence of causation rather than just correlation.”

“It would be helpful to know if the immunological response is the main driving factor in reducing dementia risk,” he added. “If it is, then further investigation could lead to new treatments.”