Shingles Vaccine Tied to 24% Lower Dementia Risk in Study of Older Adults

Older adults who received the newer shingles vaccine were substantially less likely to be diagnosed with dementia over the following four years than those who did not, according to a large observational study published this week in the journal Annals of Internal Medicine. The analysis, drawn from Medicare records and clinical data on more than half a million older adults, adds to a growing body of research linking the shingles vaccine to a lower risk of cognitive decline, though the authors caution it does not prove the vaccine causes the effect.

The study looked specifically at Shingrix, the recombinant zoster vaccine that has largely replaced an older, live-virus shingles vaccine since its introduction in 2017. Researchers led by Kaleen Hayes, an assistant professor at the Brown University School of Public Health, examined health records for 509,926 adults age 66 and older who had recently stayed in a skilled nursing facility, a population with elevated risk for both shingles and dementia.

The numbers

Of the study group, 8,843 people, or 1.7%, received at least one dose of Shingrix within 12 months of their nursing facility stay. Over four years of follow-up, 18.8% of vaccinated adults went on to receive a dementia diagnosis, compared with 24.6% of those who were not vaccinated. That gap translates to a 24% lower relative risk of dementia among the vaccinated group, and the researchers estimate it could amount to roughly one dementia case prevented for every 17 people vaccinated.

The study used a design called target trial emulation, which applies the logic of a randomized trial to observational data in an effort to reduce bias. The researchers adjusted for differences in age, sex and underlying health conditions between the two groups, since people who chose to get vaccinated tended to be somewhat younger and healthier. According to the study, those adjustments did not fully account for the association between vaccination and lower dementia risk.

How the evidence has built up

The new findings extend a line of research that began with older, live-virus shingles vaccines. A widely cited 2025 study in the journal Nature, led by researchers at Stanford, used a natural experiment created by Wales's vaccination eligibility rules and found that adults who received that earlier vaccine were about 20% less likely to develop dementia over seven years. The Brown-led study is among the first to test whether the same pattern holds for Shingrix, the recombinant vaccine that the Centers for Disease Control and Prevention now recommends in two doses for immunocompetent adults 50 and older, regardless of whether they have had shingles before.

Uptake of that recommendation has climbed steadily but remains far from universal. National survey data compiled by the CDC's AdultVaxView program show that coverage with both recommended doses of the recombinant vaccine among adults 50 and older rose from 1.1% in 2018, the year after the vaccine reached the market, to 24.1% by 2023.

Researchers do not yet have a settled explanation for why a vaccine against a skin-and-nerve virus might affect the brain. "It's probably multifactorial," Hayes told CIDRAP News, a publication of the University of Minnesota's Center for Infectious Disease Research and Policy. "When you think of a shingles case, there may be higher risks of strokes," and protecting people from strokes and related vascular events could in turn lower their dementia risk, she said. Researchers have separately theorized that the vaccine might reduce a buildup of amyloid plaques and neurofibrillary tangles, the brain changes associated with Alzheimer's disease, though Hayes said the evidence for that pathway is thinner.

The study population was drawn entirely from people who had recently left a skilled nursing facility, a group that skews older, frailer and at higher baseline dementia risk than the general population of vaccine-eligible adults. Hayes said her team chose that setting precisely because it is usually left out of research. "This population [is] really understudied, completely excluded from trials and also not even included in a lot of real world studies," she told CIDRAP News. Dementia, meanwhile, already affects an estimated 6.7 million older Americans with Alzheimer's disease alone, according to the CDC, and that figure is expected to nearly double by 2060 as the population ages, making even a modest, unproven reduction in risk a subject of intense interest to patients, families and clinicians.

What researchers are saying

Hayes said the population studied sets this analysis apart from earlier work on the subject. "This study looks at the newest vaccine only in an older, vulnerable adult population," she said, according to a statement released by Brown University. She noted that most prior research examining a possible link between shingles vaccination and dementia had focused on the older, live-virus vaccine rather than Shingrix.

"This translates to about one in 17 dementia cases potentially being prevented. Our cognition is so tied to our overall health and what happens to us physically."

That quote, also from Hayes, points to a broader theme running through the newer wave of dementia research: a widening view that brain health cannot be cleanly separated from infections, vaccinations and other physical exposures over a person's lifetime. Hayes told CIDRAP News she and her colleagues "were honestly taken aback by the results," adding that the findings "actually are consistent with other studies that have primarily included the older form of the vaccine."

The study disclosed that GlaxoSmithKline, which manufactures Shingrix, funded the research. The authors stated that the company had no role in the study's design, its analysis or the decision to publish the results, a standard disclosure practice for industry-funded research appearing in peer-reviewed journals.

What comes next

The authors and independent scientists agree that observational data of this kind, however large and carefully adjusted, cannot establish that the vaccine directly lowers dementia risk. People who seek out vaccination differ from those who do not in ways that statistical adjustment cannot fully capture, a limitation that applies to this study as it did to the earlier Welsh data set that produced similar findings for the older vaccine. Confirming a causal effect would require a randomized controlled trial that follows healthy adults for years after assigning some to receive the vaccine and others a placebo, a study that has not yet been conducted for either shingles vaccine and dementia specifically. "It really is time for a trial to get this squared away," Hayes told CIDRAP News.

In the meantime, the CDC's vaccination recommendation for adults 50 and older is unchanged and was not made on the basis of dementia prevention; it rests on Shingrix's established effectiveness against shingles itself and the painful nerve condition, postherpetic neuralgia, that can follow it. Whether the vaccine also turns out to modestly reduce dementia risk is a question the authors say will need further study, including randomized trials, to settle.