A study found that the shingles vaccine can significantly reduce the risk of dementia in old age. With few ways to reliably prevent dementia, it is drawing attention as a potential new solution.
Researchers at the Stanford University School of Medicine said that a reanalysis of large-scale medical records of about 280,000 older adults in Wales, United Kingdom, showed that people who received the shingles vaccine had a 20% lower chance of developing dementia over the next seven years than those who did not. The findings were published on the 2nd in the international journal "Cell."
About 55 million people worldwide live with dementia, and more than 10 million new patients are diagnosed each year. The most common type, Alzheimer's dementia, is known as a disease in which abnormal protein aggregates accumulate in the brain and destroy nerve cells.
For decades, scientists have tried to treat or prevent these protein changes, but clear results have been elusive. As a result, researchers have recently turned in a new direction: the hypothesis that viral infections affecting the nervous system may increase the risk of dementia. The shingles virus is among the candidates.
The team analyzed seven years of medical records for about 280,000 older adults ages 71 to 88 in Wales with no history of a dementia diagnosis. They found that vaccinated individuals had a 37% lower risk of shingles and a 20% lower risk of a dementia diagnosis compared with those unvaccinated. As of 2020, 1 in 8 people in the entire cohort had been diagnosed with dementia, but the incidence was noticeably lower in the vaccinated group.
The researchers also found the effect did not stop at prevention. The occurrence of mild cognitive impairment (MCI), considered an early stage of dementia, was also lower among those vaccinated. In particular, people who were vaccinated after already being diagnosed with dementia had lower dementia-related mortality. Over nine years of follow-up, about 50% of unvaccinated patients died from dementia, compared with about 30% among those vaccinated.
Interestingly, the protective effect against dementia was greater in women than in men. The team suggested possibilities such as generally stronger immune responses in women and the higher prevalence of shingles among women.
What makes this study distinctive is a unique vaccination policy implemented in Wales. In September 2013, facing a vaccine shortage, the government offered one year of free vaccination only to people turning 79 that year. In contrast, residents who were already 80 or older at the time were never eligible.
As a result, the researchers could compare two groups whose eligibility depended on a birthday difference of just one week. Nearly all conditions—age, education level, lifestyle, and underlying diseases—were the same, creating an effectively "randomly assigned" setup. The team called this "a natural experiment condition very close to a randomized clinical trial."
However, the exact reason remains unclear. The specific mechanism by which the vaccine reduces dementia risk is also uncertain. The researchers emphasized that further studies are needed, citing possibilities such as suppression of viral reactivation, broader activation of the immune system, or other biological pathways not yet identified.
The team plans to formally verify the vaccine's effect on dementia through large-scale randomized clinical trials. Professor Pascal Geldsetzer said, "The biggest hope is that we can test the possibility of preventing dementia with a single injection that has already been proven safe," adding, "We want to confirm causality through large-scale randomized clinical trials."
References
Cell (2025), DOI: https://doi.org/10.1016/j.cell.2025.11.007