A surprising public health policy in Wales has provided strong evidence that a vaccine could reduce the risk of dementia. In a major new study led by Stanford Medicine, researchers found that older adults who received the shingles vaccine were 20% less likely to develop dementia over the next seven years than those who didn’t get the shot.
This is the clearest sign yet that a vaccine might help prevent one of the world’s most feared brain diseases.
The study was published in the scientific journal Nature and included health data from more than 280,000 older adults in Wales.
Shingles is a painful skin rash caused by the varicella-zoster virus—the same virus that causes chickenpox. After a person recovers from chickenpox, the virus doesn’t leave the body. Instead, it stays hidden in the nervous system and can reactivate years later as shingles, especially in older adults or those with weakened immune systems.
Meanwhile, dementia affects more than 55 million people globally, with 10 million new cases each year. Most dementia research has focused on changes in the brain like plaques and tangles found in Alzheimer’s disease.
But these studies have not led to major breakthroughs in prevention. As a result, scientists are now exploring new ideas—including whether viral infections like shingles might play a role.
Past studies hinted at a link between shingles vaccines and lower dementia rates, but those findings were hard to trust. That’s because people who get vaccines tend to live healthier lifestyles in general—they might eat better, exercise more, or get regular checkups—and that could be what’s really protecting them from dementia.
These habits usually don’t show up in health records, making it hard to separate the true effect of the vaccine.
But the situation in Wales created what scientists call a “natural experiment.” In 2013, the country began a shingles vaccination program for people who were exactly 79 years old on a specific date, September 1. People who were 80 or older were excluded and would never become eligible.
This unique rule meant that people born just days apart were treated very differently. Some were offered the vaccine, while others just missed out—not because of their health or choices, but because of a strict cutoff.
The researchers took advantage of this to compare people just before and after the age cutoff. These individuals were nearly identical in age and health habits, but only one group could receive the vaccine. That made the study results much more reliable, like a randomized trial without needing to assign people to groups.
About half of the eligible people actually got the vaccine, while almost none of the ineligible group did. The researchers found that those who got vaccinated had a 37% lower chance of getting shingles—just as expected. But they were also 20% less likely to develop dementia over the next seven years.
Even more striking, this strong protective effect showed up no matter how the data was analyzed. The two groups were the same in terms of education, health conditions like heart disease or diabetes, and other medical treatments. The only difference was access to the shingles vaccine.
The researchers also noticed that the vaccine’s protection against dementia was stronger in women than in men. That could be because women tend to have stronger immune responses to vaccines and are more likely to get shingles.
It’s still unclear exactly how the vaccine works to protect the brain. It might reduce the virus’s ability to damage the nervous system, or it could trigger a broader immune response that helps prevent cognitive decline.
The type of vaccine used in the study is no longer available, but it’s possible that newer, more effective shingles vaccines might provide even better protection. The research team has already found similar results in health records from England, Australia, New Zealand, and Canada.
Still, the scientists want even stronger proof. They’re now planning a randomized trial where some people would receive the shingles vaccine and others would get a placebo. Because the vaccine is already known to be safe, the trial could be simple and fast. The team is seeking funding to make it happen.
One hopeful sign: in the Wales study, the protective effect of the vaccine began to appear just 18 months after people received it. That means a future trial might not take long to show whether the vaccine truly helps prevent dementia.
This study offers one of the strongest arguments so far that a vaccine may help prevent dementia. It uses a clever design that avoids the common problem of bias found in most observational studies. The 20% lower dementia rate in vaccinated people, especially with no other major differences between groups, is both impressive and promising.
If these findings are confirmed in a randomized trial, we could have a simple, safe, and widely available tool to help reduce the risk of dementia—something no current drug can do. This research also strengthens the growing theory that viruses and the immune system play a key role in cognitive decline, opening new doors for dementia prevention.
For now, it may be too early to recommend the shingles vaccine solely to prevent dementia. But the evidence is growing, and future studies may soon change the way we think about protecting our brains as we age.
If you care about brain health, please read studies about how the Mediterranean diet could protect your brain health, and blueberry supplements may prevent cognitive decline.
For more information about brain health, please see recent studies about antioxidants that could help reduce dementia risk, and Coconut oil could help improve cognitive function in Alzheimer’s.
The research findings can be found in Nature.
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