Getting vaccinated against shingles can reduce the risk of dementia, according to a new study led by Stanford researchers.
The study, published in Nature on Wednesday, found that older adults who received the shingles vaccine were 20% less likely to develop dementia in the subsequent seven years than those who did not receive the vaccine.
The findings build on a growing body of evidence suggesting that viruses that affect the nervous system — like the varicella-zoster virus that causes shingles — can increase the risk of dementia, and that preventing them may help lower the risk of dementia.
The study included about 280,000 older adults in Wales, aged 79 to 88, who did not have dementia at the start of the country’s shingles vaccination program in September 2013. Those who got vaccinated received the live-attenuated vaccine Zostavax, an older shingles vaccine that was in use at that time — not the newer vaccine, Shingrix, which was not rolled out until several years later and is currently being used in many countries including the United States. Shingrix is more effective and long-lasting than Zostavax, which has since been discontinued.
Previous studies have found associations between shingles vaccination and lower dementia rates, but could not rule out whether other factors like diet and exercise were what contributed to lower dementia risk. People who get vaccinated, for instance, are often more health-conscious in general and more likely to adhere to a healthy diet and exercise regimen, which reduces dementia risk.
The newly published study sought to remove that bias by taking advantage of a “natural experiment” — Wales imposed a strict age requirement for the vaccine at the start of the rollout because there was limited supply of the shots at the time. People who were 79 were eligible for one year, but people who were 80 or older were not eligible. This established two comparison groups, of very similar ages, where the main difference was whether they were eligible to get vaccinated or not.
About half of people in the eligible group got vaccinated; almost no one in the ineligible group got vaccinated.
“Our study shows for the first time that there really seems to be a cause and effect relationship between shingles vaccination and a protective effect on dementia,” said senior author Pascal Geldsetzer, an assistant professor of medicine at Stanford. “That appears to be a large protective effect that is of big importance to population health, dementia care and research into dementia and what causes dementia.”
It’s not clear why the shingles vaccine appears to protect against dementia, but there are some potential explanations. Shingles is caused by the same virus that causes childhood chickenpox, and it usually stays dormant in nerve cells for years. When the virus gets reactivated — usually in older adulthood, and often triggered by stress or a weakened immune system — it causes neuroinflammation, which is thought to contribute to dementia.
“So reducing the reactivation and therefore the inflammation could be a good thing,” Geldsetzer said.
Another theory is that the vaccine elicits a broader immune response beyond just the specific antibody responses it’s designed to elicit, and that could have benefits for dementia and other chronic diseases.
Geldsetzer said similar benefits for dementia have been observed in other countries that rolled out Zostavax, including the United Kingdom, Scotland and Australia. But what’s needed is a large randomized clinical trial to prove it; he is seeking philanthropic and private foundation funding to pursue such a trial because Zostavax has been discontinued.