Scientists found a vaccine that cuts dementia risk by 20%. It's not the one you'd think.

A vaccine millions of Americans already receive to prevent a painful rash may also be quietly protecting their brains from dementia. New research continues to strengthen the connection between the shingles vaccine and reduced Alzheimer's risk, with studies showing recipients have up to 20% lower odds of developing the devastating neurological condition.

The findings have caught the medical community's attention because they suggest a potential new avenue for dementia prevention, one that's already FDA-approved and widely available.

What the research reveals

A landmark study published in Nature in April 2025 found that people in Wales who received the shingles vaccine were 20% less likely to develop dementia over a seven-year follow-up period. The research, led by Stanford University scientists, used a natural experiment created by the country's age-based eligibility rules for vaccination.

According to the study, the vaccine reduced the probability of a new dementia diagnosis by 3.5 percentage points compared to unvaccinated individuals. In a follow-up study published in Cell in December 2025, the same team found even more striking results: the vaccine may also slow disease progression in people already living with dementia.

"It was a really striking finding," said Dr. Pascal Geldsetzer, assistant professor of medicine at Stanford and senior author of the studies, in statements to Stanford Medicine News. "This huge protective signal was there, any which way you looked at the data."

Why the shingles vaccine specifically

Scientists have several theories about why this particular vaccine might protect the brain. The varicella-zoster virus, which causes both chickenpox and shingles, remains dormant in the nervous system after initial infection. Even while dormant, according to CNN Health, the virus causes ongoing inflammation that may contribute to cognitive decline.

"We know this causes inflammation in the nervous system, and we know inflammation is a key process in so many chronic diseases, including dementia," Geldsetzer explained. "So it makes sense that reducing these reactivations through shingles vaccination may have benefits for the dementia disease process."

Additionally, vaccines may provide broader immune system benefits beyond targeting specific infections. Research published in Nature Medicine in October 2025 demonstrated a consistent relationship between virus reactivation and dementia risk across more than 100 million health records.

Who should consider this information

The CDC already recommends the shingles vaccine for adults 50 and older, regardless of whether they remember having chickenpox. According to CDC guidelines, two doses of Shingrix are more than 90% effective at preventing shingles and its complications.

Experts caution that while the dementia findings are promising, they don't yet prove the vaccine directly prevents cognitive decline. The studies are observational, meaning they show correlation rather than definitive causation. However, given the vaccine's established safety profile and primary benefits, the potential brain protection represents an encouraging bonus.

"People shouldn't get vaccinated solely for dementia prevention at this point," Geldsetzer noted. "But if you were on the fence about getting your shingles vaccine, this is another compelling reason to talk to your doctor."

What's next

Clinical trials specifically designed to test whether the shingles vaccine prevents dementia are now being planned. These prospective studies will provide more definitive answers about causation and could potentially lead to new recommendations for dementia prevention.

Meanwhile, researchers are investigating whether other vaccines might offer similar neuroprotective benefits, as studies have also shown associations between flu vaccines and reduced dementia risk. The emerging field of "vaccine-preventable dementia" could reshape how physicians approach brain health in aging populations.

For the 7.2 million Americans currently living with Alzheimer's disease, according to the Alzheimer's Association, and the millions more at risk, even a 20% reduction in odds would represent a significant public health breakthrough, especially from a vaccine that's already sitting on pharmacy shelves.