Older adults who got a shingles vaccine after a stay in a skilled nursing facility were diagnosed with dementia less often over the following four years than those who went unvaccinated, according to a study published in June in Annals of Internal Medicine that has continued to draw attention from health outlets this month.
Researchers led by Kaleen Hayes of Brown University's School of Public Health used Medicare claims and electronic health records covering more than 5,500 skilled nursing facilities nationwide, identifying 509,926 adults age 66 and older admitted between 2017 and 2022. Only 8,843 of them received the recombinant shingles vaccine, sold as Shingrix, during the study window. Among the vaccinated group, 18.8% were diagnosed with dementia within four years, compared with 24.6% of those who were not vaccinated — a 24% lower relative risk.
A statistical technique, not a clinical trial
Because no one randomly assigned some patients to get the vaccine and others not to, the researchers used a method called target trial emulation, which tries to mimic the structure of a randomized trial using observational data by carefully matching vaccinated and unvaccinated patients on age, health status and other factors. Even with that adjustment, the authors were careful to note what their method cannot show.
Vaccinated patients tended to be somewhat younger and in better general health than those who skipped the shot, and while the statistical matching was designed to account for that gap, the authors acknowledged it could still explain part of the association. The study is observational, not a controlled trial, and it cannot establish that the vaccine itself lowers dementia risk rather than simply identifying a group of patients who were, on average, healthier or more engaged with preventive care to begin with.
It's really amazing to see that something that's supposed to prevent a physical ailment can also help keep our brain healthy, too.
Kaleen Hayes, Brown University School of Public Health
The finding fits a growing body of research, including earlier work out of Wales and England, that has linked shingles vaccination to lower dementia rates. One hypothesis is that the herpes zoster virus, which causes shingles and lies dormant in the nervous system after chickenpox infection, may contribute to neuroinflammation when it reactivates in older adults, and that preventing outbreaks could reduce that damage. That mechanism remains unproven. GSK, which manufactures Shingrix, helped fund the study but the company did not control its design, analysis or publication, according to the authors.
The researchers say the results strengthen the case for a randomized clinical trial that could determine whether the vaccine actually protects the brain or is merely a marker of a healthier patient population. Until such a trial is completed, public health officials continue to recommend the shingles vaccine primarily for its established purpose: preventing a painful viral illness that becomes more common with age.
