A unique public health policy in Wales has provided some of the strongest evidence yet that a vaccine could help lower the risk of dementia.
A new study, led by Stanford Medicine and published in Nature on April 2, found that older adults in Wales who received the shingles vaccine were 20% less likely to develop dementia over the next seven years than those who did not.
Why shingles might matter for brain health
Shingles is caused by the varicella-zoster virus — the same virus that causes chickenpox.
After an initial chickenpox infection, usually in childhood, the virus stays dormant in nerve cells for life. In older adults or those with weakened immune systems, the virus can reactivate, causing a painful rash known as shingles.
Dementia affects more than 55 million people worldwide, with 10 million new cases each year. While most dementia research has focused on Alzheimer’s disease and its hallmark brain changes (plaques and tangles), some scientists are exploring whether viral infections that affect the nervous system might also play a role.
A rare “natural experiment” in Wales
In 2013, Wales introduced a shingles vaccination program that made anyone who was exactly 79 years old on September 1, 2013 eligible for the vaccine for one year. People who were 80 or older on that date were never eligible.
This age cut-off, designed to ration the limited supply, created a situation where two nearly identical groups — separated only by a few days or weeks in birth date — had very different access to the vaccine.
By comparing health outcomes in these groups, researchers could closely approximate a randomized controlled trial and reduce the bias that often affects vaccine studies (for example, the fact that people who choose vaccination are often more health-conscious).
Study details and results
The research team examined health records from over 280,000 Welsh adults aged 71 to 88, focusing on those closest to the eligibility cut-off. About half of eligible people received the vaccine, compared with almost none of those ineligible.
Over seven years:
– The vaccine reduced shingles cases by 37%.
– Those who received the vaccine were 20% less likely to develop dementia.
Importantly, the two groups were otherwise similar in education, other vaccinations, and rates of common health conditions. The only major difference was the drop in dementia diagnoses among the vaccinated.
Stronger effect in women
The study also found that women benefited more than men from the dementia protection.
This could be due to stronger immune responses in women or differences in how dementia develops. Women are also more likely to develop shingles.
Researchers don’t yet know exactly how the vaccine reduces dementia risk. It could be by preventing shingles flare-ups, boosting the immune system, or another mechanism. They also don’t know whether the newer, more effective shingles vaccine — which contains only parts of the virus — would have the same or stronger effects.
The team has replicated the findings in health records from other countries, including England, Australia, New Zealand, and Canada. They now want to run a large randomized controlled trial, which could provide the clearest proof of cause and effect.
Since the older live-attenuated vaccine is no longer manufactured, philanthropic funding would be needed to make such a trial happen.
If you care about dementia, please read studies about Scientists find a simple solution to fight dementia and findings of Big causes of memory loss, dementia you need to know.
For more about dementia, please read studies about People who take high blood pressure medications have lower dementia risk and findings of Early indicators of dementia: 5 behaviour changes to look for after age 50.
The study is published in Nature.
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