A study of more than 500,000 older adults found a lower four-year dementia risk among those who received the recombinant shingles vaccine.
Researchers used electronic health records and Medicare data to compare vaccinated and unvaccinated nursing home residents.
The findings are promising, but they don’t prove the vaccine prevents dementia, and more research is needed.
Getting a shingles shot could potentially offer benefits beyond protecting against the painful rash caused by reactivation of the chickenpox virus.
New research led by University of Delaware epidemiologist Daniel Harris found that older adults who received a shingles vaccine had a lower risk of developing dementia over the following four years.
The study, published in Annals of Internal Medicine, looked specifically at older adults who had recently been admitted to skilled nursing facilities. Researchers found that those who received at least one dose of the recombinant herpes zoster vaccine had a 24% lower relative risk of developing dementia compared with those who didn't receive the vaccine.
The finding adds to earlier research linking shingles with cognitive decline. However, the researchers caution that the study was observational, meaning it can't establish that vaccination itself prevented dementia.
“There’s a lack of randomized trial evidence on the potential effects of the shingles vaccine on dementia risk, but there are methodological and analytical tools at our disposal to generate evidence in real-world databases; however, there are still threats to validity,” Harris said in a news release.
How researchers studied the connection
The research team analyzed Medicare claims linked with electronic health records from more than 500,000 people who entered skilled nursing facilities between 2017 and 2022. Participants were at least 66 years old, had no previous dementia diagnosis, and were eligible to receive the recombinant shingles vaccine.
About 8,800 participants received at least one vaccine dose within a year of entering the facility. Most of those vaccinations actually happened after the person had left the facility.
Because people who choose to get vaccinated can differ from those who don't, the researchers used a method called target trial emulation to make the comparison more like a randomized clinical trial. They accounted for 57 baseline and changing health characteristics and also conducted "negative control" analyses to look for signs of remaining bias.
What the results mean for consumers
Over four years, dementia was diagnosed in about 18.8% of people who received at least one dose of the recombinant vaccine, compared with 24.6% of those who didn't receive it. That's a difference of about 5.8 percentage points, or a 24% lower relative risk.
The researchers say the results remained after additional analyses, although the negative-control tests suggested some residual confounding. In other words, there may still be differences between vaccinated and unvaccinated people that the researchers couldn't fully measure or account for.
“Vaccines do more than help prevent the infection they’re originally intended to protect against,” said Harris. “They help prevent the consequences of infection.”
For consumers, the study offers another reason researchers are interested in shingles vaccination, but it shouldn't be interpreted as proof that getting vaccinated will prevent dementia. Harris and his colleagues say randomized trials are still needed to establish whether the vaccine itself has a protective effect against dementia.