Researchers found that people who received at least one dose of the recombinant shingles vaccine had a 24% lower risk of dementia compared with those who were not vaccinated.

The study analysed health records and Medicare data from more than 500,000 adults aged 66 and older who had been admitted to skilled nursing facilities.

The research focused on 509,926 people admitted to more than 5,500 skilled nursing facilities across the United States between 2017 and 2022. Among them, 8,843 received the Shingrix vaccine.

After four years of follow-up, dementia was diagnosed in 18.8% of vaccinated participants, compared with 24.6% among those who remained unvaccinated.

Researchers estimated that the difference could translate to approximately one dementia case potentially prevented for every 17 people vaccinated.

The study was led by Kaley Hayes, an assistant professor at Brown University’s School of Public Health, together with researchers from Brown University, the University of Delaware, the Providence Veterans Affairs Medical Center and other institutions.

The researchers used a method known as target trial emulation, which attempts to reproduce some of the conditions of a randomised clinical trial using existing health data. Participants were eligible for shingles vaccination and had no previous diagnosis of dementia.

The findings add to previous research that has also observed a relationship between shingles vaccination and a lower risk of dementia. Scientists say this has raised the possibility that vaccines designed to prevent infections could have additional effects on brain health.

However, researchers caution that the findings should not be interpreted as proof that the shingles vaccine prevents dementia.

Because the study was observational, it cannot establish a direct cause-and-effect relationship.

People who received the vaccine were generally slightly younger and healthier than those who did not, although researchers adjusted their analysis for these differences and found that they did not fully explain the association.

Further research, particularly clinical trials, will be needed to determine whether Shingrix itself directly reduces the risk of dementia.

The study was published in the Annals of Internal Medicine. The researchers also disclosed that the study received funding from GlaxoSmithKline, the manufacturer of Shingrix, although they reported that the company had no control over the study's design, analysis or publication decision.