Shingles Vaccine and Brain Health: What the Research Shows
Researchers first noticed the potential link between shingles vaccination and brain health in a natural experiment study that analyzed health records from more than 280,000 older adults living in Wales. (A natural experiment is an observational study that uses real-world policies to create comparison groups that are otherwise very similar.) The people studied had received the live-attenuated (weakened) herpes zoster vaccine (Zostavax), which was discontinued in the United States in 2020 and replaced by the more effective recombinant zoster vaccine (Shingrix), which does not use a live form of the virus.
For this group of people in Wales, shingles vaccine eligibility was determined by birth date as of September 2013. People who were age 80, born before September 2, 1933, were not eligible for vaccination, while those born on or after that date were, providing researchers with the opportunity to do a large-scale study comparing vaccinated and unvaccinated people. The study found that at follow-up seven years later, those who received the vaccine had a 20 percent lower risk of developing dementia. The researchers said the study was as close to a randomized, controlled trial — considered the gold standard in research, in which a treatment group is compared with a control group who received no treatment — as you could get without conducting one.
And the research on the link has grown, according to Jason Tetro, a microbiologist in Edmonton, Canada, and the author of The Germ Files and The Germ Code. “Since then other studies have either confirmed or added more valuable information to show that getting the shingles vaccine does indeed help to reduce the risk or severity of dementia,” he says.
A follow-up study suggested that shingles vaccination was linked not only to lower dementia diagnoses but to possibly slowing the progression of dementia in people who already had it. They found fewer cases of mild cognitive impairment, which raises the risk of dementia, and overall lower dementia-related death in people already diagnosed with the progressive illness.
And research on the newer recombinant zoster vaccine has shown that, like the previous live vaccine, it significantly lowers the risk of dementia in the six years following vaccination. One study found that it was also associated with a 17 percent delay in dementia diagnosis among those who were eventually affected. Because this vaccine is newer, there isn’t as much data, though research is ongoing.
Conversely, research has found that people who experienced shingles had about a 20 percent higher risk of later reporting cognitive decline. In a separate observational study following more than 149,000 middle-aged and older adults for over a decade, researchers noted that those who had the virus reactivate were more likely to report early cognitive impairment symptoms, such as memory lapses and confusion that can indicate dementia later on.
While these findings are promising, evidence is still evolving and has a long way to go before the vaccine is recommended to prevent or treat dementia, says William Schaffner, MD, a professor of infectious diseases at Vanderbilt University in Nashville, Tennessee, and a spokesperson for the Infectious Diseases Society of America.
He calls the research “early, but accumulating. It’s provocative, it’s exciting, and it’s absolutely fascinating” from the point of view of how a disease develops.
Researchers are still working to understand the link, though. “The question right now is why – that’s what we’re not totally sure of,” says Ankush Bansal, MD, a lifestyle medicine physician and hospitalist in Westlake, Florida.
One leading theory centers on inflammation, Dr. Bansal says. When the varicella-zoster virus reactivates later in life as shingles, it triggers a widespread inflammatory response in the body. That inflammation goes beyond skin deep, affecting the nervous system and, potentially, the brain.
“Inflammation from shingles may contribute to vascular damage and neurological effects, and reducing that inflammatory burden may lower long-term risk,” he says.