Shingles Vaccine May Lower Dementia Risk and Slow Disease Progression, Major Studies Suggest

New research from Stanford University Medical Center is drawing serious attention in the medical and public health communities, suggesting that a widely used shingles vaccine may do more than prevent a painful viral infection. According to large-scale studies published in Nature and Cell, receiving the shingles vaccine is associated with a significantly lower risk of developing dementia and may even slow the progression of dementia in people already diagnosed with the condition.

These findings are especially striking because dementia has long resisted effective prevention and treatment strategies, despite decades of intense research. If confirmed further, this work could point to a readily available preventive intervention for one of the world’s most challenging neurodegenerative conditions.

A Natural Experiment That Changed the Evidence Landscape

One of the biggest challenges in studying vaccines and dementia is bias. People who get vaccinated often have healthier lifestyles overall—they may exercise more, eat better, and seek medical care more regularly. These factors are hard to measure accurately in health records, making it difficult to know whether lower dementia risk is truly caused by vaccination.

What makes this research different is a unique public health policy in Wales that unintentionally created a near-perfect natural experiment.

In September 2013, Wales introduced a shingles vaccination program using a live-attenuated varicella-zoster vaccine. Due to limited supply, eligibility was strictly determined by age. Individuals who were 79 years old at the start of the program could receive the vaccine for one year. Those who were 80 or older at that time were never eligible.

This seemingly small age cutoff produced a powerful research opportunity. People born just weeks apart—otherwise statistically similar in education, health status, and behavior—were split into two groups: those who could receive the vaccine and those who could not.

Researchers compared people who turned 80 just before the cutoff with those who turned 80 just after. This approach allowed them to isolate the effects of vaccine eligibility with minimal bias, creating conditions close to a randomized controlled trial, without actually running one.

The Scale of the Study and What It Found

The research team analyzed health records from more than 280,000 Welsh adults aged 71 to 88 who did not have dementia when the vaccination program began. About half of those eligible actually received the vaccine, while almost none of the ineligible group did.

Over the following seven years, the results were clear and consistent:

People who received the shingles vaccine were about 20% less likely to develop dementia than those who did not.
By 2020, roughly one in eight individuals in the study had been diagnosed with dementia, but rates were significantly lower in the vaccinated group.
The vaccine also reduced cases of shingles itself by around 37%, matching results from earlier clinical trials.

Importantly, researchers carefully examined other possible explanations. They found no meaningful differences between vaccinated and unvaccinated groups in education levels, rates of diabetes, heart disease, cancer, or use of other preventive healthcare services. The reduction in dementia diagnoses stood out as the only major difference.

Benefits May Extend Beyond Prevention

The research did not stop with dementia prevention. Using the same Welsh data, scientists examined outcomes for people who already had dementia when the vaccination program began.

The results were unexpected and promising:

Vaccinated individuals were less likely to progress from mild cognitive impairment to full dementia during long-term follow-up.
Among people who already had dementia, those who received the vaccine were far less likely to die from dementia-related causes over the next nine years.
Nearly half of unvaccinated dementia patients died from dementia during follow-up, compared to about 30% of vaccinated patients.

These findings suggest that the shingles vaccine may have therapeutic potential, not just preventive effects. In other words, it may help slow the course of the disease, even after dementia has begun.

Why Shingles and Dementia Might Be Connected

Shingles is caused by the varicella-zoster virus, the same virus responsible for chickenpox. After childhood infection, the virus remains dormant in nerve cells for life. In older adults or those with weakened immune systems, it can reactivate, causing shingles.

Dementia affects more than 55 million people worldwide, with nearly 10 million new cases each year. Traditional dementia research has focused heavily on brain plaques and tangles, particularly in Alzheimer’s disease. However, these approaches have not yet delivered major breakthroughs in prevention.

An emerging theory suggests that viruses affecting the nervous system may play a role in triggering or accelerating neurodegeneration. The shingles vaccine could reduce dementia risk by:

Preventing viral reactivation in nerve cells
Reducing chronic inflammation in the brain
Stimulating broader immune responses that protect neural tissue

The exact mechanism remains unknown, but the consistency of the findings across multiple datasets strengthens the case that the effect is real.

Stronger Protective Effects Observed in Women

One notable detail in the data is that the protective effect of the vaccine was much stronger in women than in men.

This difference may be related to sex-based immune responses. Women generally produce higher antibody levels after vaccination and are also more likely to develop shingles. There may also be biological differences in how dementia develops and progresses between sexes.

While the reasons are still being studied, this finding highlights the importance of considering sex-specific responses in future dementia research.

Replicated Across Multiple Countries

The Welsh study did not stand alone. Researchers replicated their findings using health records from England, Australia, New Zealand, and Canada, all of which had similar shingles vaccine rollouts.

Across these countries, the same pattern emerged: shingles vaccination was consistently associated with lower dementia rates. This repeated signal across different populations adds confidence that the observed effects are not due to chance or local factors.

What We Still Don’t Know

Despite the strength of the evidence, some questions remain unanswered:

The studies used a live-attenuated shingles vaccine, which is no longer the most common option in many countries.
It is unclear whether newer recombinant vaccines, such as Shingrix, provide the same or greater dementia-related benefits.
While the natural experiment design greatly reduces bias, it does not fully replace a randomized controlled trial.

Researchers are now advocating for a large-scale clinical trial, where participants would be randomly assigned to receive the live-attenuated vaccine or a placebo. Because the vaccine is already known to be safe and requires only a single dose, such a trial could produce results relatively quickly.

A Potential Shift in Dementia Prevention Strategy

If future trials confirm these findings, the implications would be profound. Dementia prevention strategies could expand beyond lifestyle changes and experimental drugs to include routine vaccination programs already in place.

At a time when dementia cases are rising rapidly and treatment options remain limited, the possibility that a decades-old vaccine could reduce risk and slow disease progression is both surprising and encouraging.

Research References:
Nature study (April 2025): https://www.nature.com
Cell study (December 2025): https://www.cell.com/cell/fulltext/S0092-8674(25)01256-5