Could a vaccine prevent dementia? Shingles shot data only getting stronger.

While lifesaving vaccines face a relentless onslaught from the Trump administration—with fervent anti-vaccine advocate Robert F. Kennedy Jr. leading the charge—scientific literature is building a wondrous story: A vaccine appears to prevent dementia, including Alzheimer’s, and may even slow biological aging.

For years, study after study has noted that older adults vaccinated against shingles seemed to have a lower risk of dementia. A study last month suggested the same vaccine appears to slow biological aging, including lowering markers of inflammation.

“Our study adds to a growing body of work suggesting that vaccines may play a role in healthy aging strategies beyond solely preventing acute illness,” study author Eileen Crimmins, of the University of Southern California, said.

Another study this month suggested the positive findings against dementia from the past may even be underestimates of the vaccination’s potential, with a newer vaccine against shingles providing even more protection.

Shingles

If the dementia protection is real, it’s a fluke. The vaccine was designed for the entirely unrelated task of keeping the varicella-zoster virus—the cause of chickenpox (varicella)—from reactivating and causing an agonizing rash.

Anyone who suffered the itchy childhood affliction carries the virus with them for the rest of their lives, largely dormant in their nerve cells. But, if it awakens, it causes a painful, itchy rash—aka shingles (herpes zoster). The rash develops fluid-filled blisters and crusts over, lasting for days to several weeks. For some, it can be intensely painful, and the pain can linger for months or even years after the rash fades. If it occurs near the eye, it can cause permanent vision damage; near the ear, it can cause permanent hearing and balance problems.

Shingles is thought to be triggered by a fault in the immune response that keeps the latent virus in check, often from age-related decline. That’s where a vaccine comes in. The first was Zostavax, released by Merck in 2006, which delivers a hefty dose of a live, but weakened, version of the varicella-zoster virus. This spurs the immune system to shore up defenses to prevent the virus from reigniting. Studies found the vaccine cut the risk of shingles by 51 percent.

In 2017, a new vaccine hit the scene: Shingrix, a recombinant, adjuvanted vaccine from GlaxoSmithKline. Instead of a whole, live virus vaccine like Zostavax, Shingrix delivers only a key protein found on the outside of the varicella-zoster virus particle (glycoprotein e) that re-primes the immune system. The shot also contains an adjuvant—an extra ingredient that stimulates the immune system—to ensure a vigorous response. Trials found that the response to Shingrix is indeed vigorous, with the vaccine being 90 to 97 percent effective at preventing shingles in adults age 50 and up.

With its superior efficacy, the US Centers for Disease Control and Prevention and its vaccine advisors switched its recommendation in 2018, ditching Zostavax for the more effective Shingrix.

In the meantime, researchers noted that since Zostavax’s debut, vaccinated adults seemed to be at lower risk of dementia than their unvaccinated peers. But studies comparing the vaccinated to the unvaccinated raise the question of whether the data is simply pointing to a background difference between the two groups; perhaps people who seek vaccination are generally healthier—a problem called healthy-user bias.

Natural experiments

In the past few years, studies have been putting that concern to rest. Instead of comparing vaccinated versus unvaccinated, researchers took advantage of vaccine rollouts in different countries, including Australia, Canada, and Wales. The vaccine introductions created clear cutoffs for people who were suddenly eligible for the vaccine and people who were permanently ineligible. These “natural” experiments lessened the concern of people being able to self-select their group.

So far, the results of these studies have consistently supported the finding that shingles vaccination is linked to a lower risk of dementia. The study in Wales, for instance, published in Nature in April 2025, looked at outcomes in over 280,000 older people after the September 1, 2013, debut of Zostavax. At the time, people 71 to 78 years old progressively became eligible for the vaccine, while those who were 80 at the start of the rollout were ineligible and never became eligible. Researchers looked at dementia diagnoses over a seven-year follow-up period and found that vaccination among the eligible reduced the relative rate of dementia cases by 20 percent compared with the ineligible group.

That same month, researchers published a study in JAMA that followed over 18,000 older people in Australia after the November 1, 2016, rollout of Zostavax. People 70 to 79 at that date were eligible for a free Zostavax dose. But everyone age 80 or older was permanently ineligible. After a 7.4-year follow-up period, the researchers found that 5.5 percent of the ineligible people were diagnosed with dementia, while only 3.7 percent of those in the eligible category were diagnosed with the condition, a 1.8 percentage point drop.

A third natural study out this month in The Lancet Neurology found a similar 2 percentage-point drop in dementia rates in Canada after the Zostavax rollout there.

Newer vaccine

As Eric Topol, a molecular medicine expert at Scripps Research Institute, noted, if a drug were found to cut the risk of dementia by 20 percent, it would be considered a breakthrough. But data on the shingles vaccine has been met with no such fanfare.

Still, further data suggests that vaccination may be even better than it already appeared—the rosy findings so far may be an underestimate based on the now-outdated Zostavax vaccine. With Shingrix, which is significantly more effective against shingles, the protective effect against dementia may be even larger.

In 2024, researchers reported another natural experiment comparing dementia rates among over 200,000 people in the US vaccinated before or after the switch from Zostavax to Shingrix. The study, published in Nature Medicine, found that compared with Zostavax, vaccination with Shingrix was linked to a 17 percent relative increase in dementia-free time.

A study published in Nature Communications this month by researchers in California went further. They compared dementia rates among nearly 66,000 people who received the Shingrix vaccine and over 260,000 unvaccinated matched controls. The researchers found that the vaccinated group had a 51 percent lower risk of dementia compared to the unvaccinated controls.

Lingering questions

Of course, these consistent findings on dementia prevention raise the question of how exactly the vaccine is preventing cases. Unfortunately, researchers still don’t know. However, many have speculated that by fortifying immune responses against the varicella-zoster virus and preventing reactivation, the vaccine reduces overall brain inflammation that could contribute to the development of dementia.

Another lingering question from the data so far is that several studies have found that women see more benefit from the vaccine than men in terms of dementia risk. It’s unclear why this would be the case, but researchers have noted that there are some potentially related associations: Women are more likely to develop dementia than men, and they’re also more likely to get shingles.

The study published last month, looking at biological aging after shingles vaccination, tried to address some of these questions. The study, published in the Journal of Gerontology and led by Crimmins and Jung Ki Kim, looked at blood and health markers from over 3,800 adults, about half of whom were vaccinated and half not. The researchers used tests to examine markers for inflammation, immune response, cardiovascular health, signs of neurodegenerations, and gene activity. They also created a composite biological aging score for participants.

The results suggest that vaccinated people had lower signs of inflammation and molecular aging as well as better composite aging scores. The data also hinted that vaccinated women had better results on some of the molecular aging testing.

Kim noted that chronic, low-level inflammation can contribute to age-related health conditions, including cardiovascular disease and dementia. “By helping to reduce this background inflammation—possibly by preventing reactivation of the virus that causes shingles, the vaccine may play a role in supporting healthier aging,” she suggested.

Of course, additional studies will need to confirm the findings. And if they do, the results could also be even better in follow-up studies. In Kim and Crimmins’ study, the participants were vaccinated with Zostavax, the older vaccine, not the newer, more effective Shingrix.