Scientifically Speaking: Shingles vaccine could offer dementia protection

Recent estimates suggest that about 7.4% of adults over 60 or 88 lakh people are living with dementia in India.

I received my first dose of the shingles vaccine earlier this year, and the side effects weren’t subtle. For a few days I suffered through fever, fatigue, and a sore arm in a way that I had not experienced with other recent jabs of flu shots and Covid-19 boosters.

A nurse prepares a vaccine. (Reuters File Photo)

But as I prepare for my second dose next month, I’m buoyed by new research published in Nature which suggests the shingles vaccine might offer meaningful protection from dementia.

The study by Pascal Geldsetzer and his colleagues found that receiving the shingles vaccine reduced the probability of developing dementia by 20% over a seven-year period. In an era when vaccines are often subject to controversy, this finding offers compelling evidence of beneficial effects far beyond a vaccine’s primary target disease.

Dementia affects crores of people worldwide, and its burden is rising fast as populations age. Recent estimates suggest that about 7.4% of adults over 60 or 88 lakh people are living with dementia in India.

What makes this study so brilliant is its design, which resulted from an unintentional quirk of who could get the shingles vaccines in the United Kingdom. In Wales, eligibility for the live-attenuated herpes zoster vaccine (Zostavax) was determined by an arbitrary birthdate cutoff. Those born on or after September 2, 1933, were eligible, while those born even a day earlier were not.

This created two groups of people nearly identical in every way except their likelihood of receiving the vaccine. People born just after the cutoff had nearly a 50% chance of being vaccinated, while those born just before were typically unvaccinated.

As Harvard physician-economist Anupam Jena mentioned it in a commentary in Nature, the cutoff date created “a natural experiment in which vaccine uptake was sharply divided between two groups of individuals with nearly identical ages and backgrounds.” The assignment to one group or the other, he noted, “was as good as random,” giving the study solid strength that is usually found only in gold standard medical trials.

To limit differences between groups, researchers focused their analysis on individuals born just one week on either side of the cutoff. They examined potential confounding factors like how often people visited doctors or whether they were on medications that might influence dementia risk and found no significant imbalances.

The researchers tracked over 282,000 older adults over time. Their analysis showed that receiving the vaccine reduced the probability of a new dementia diagnosis by 3.5 percentage points, which is equivalent to a hefty 20% relative risk reduction. This supports the theory that vaccines may stimulate generalised immune responses, lowering brain inflammation, which is a known contributor to dementia.

Researchers also found that people who had multiple shingles episodes were more likely to develop dementia, and that those treated with antivirals during outbreaks had a lower risk supporting the idea that viral inflammation plays a role in cognitive decline.

Another possibility is immune training. Previous studies have shown that vaccines for flu, tetanus-diphtheria, and pneumococcus also correlate with reduced dementia risk. Boosting immune function in aging adults could be a key and yet undervalued strategy for preserving brain health.

While similar studies in other countries have found comparable trends, this is among the first to use a natural experiment design, offering unusually strong evidence of a protective effect. The study didn’t distinguish between types of dementia, so it’s unclear whether the effect is stronger for Alzheimer’s disease or other forms. That’s a question that future research will be able to answer.

It’s worth noting that this study focused on Zostavax, the older live-attenuated shingles vaccine, not the newer recombinant vaccine, Shingrix, which is now more widely used (and the vaccine that I got the first dose for earlier this year).

A 2024 study published in Nature Medicine found that Shingrix was associated with a 17% increase in dementia-free survival time. Interestingly, although Shingrix is more effective at preventing shingles, more follow-up is needed to directly compare the dementia-related effects of both vaccines.

In India, both Zostavax and Shingrix are approved and available.

But even with the limitations of the study, a 20% reduction in dementia is potentially life-altering. Being able to prevent or delay memory loss means more time living independently, recognising loved ones, and avoiding long-term care. The effect was also stronger among women, which aligns with previous research showing live-attenuated vaccines often produce more robust immune responses in females.

If these findings hold, they could reshape how we think about vaccines not just as protection from disease, but as tools for preserving long-term brain health. What was once just a jab to prevent a painful rash might also be a powerful tool against cognitive decline. As I get ready for my second jab of the shingles vaccine, the side effects now seem like a small price to pay for an unexpected health benefit.

Anirban Mahapatra is a scientist and author, most recently of the popular science book, When the Drugs Don’t Work: The Hidden Pandemic That Could End Medicine. The views expressed are personal.