Shingles Vaccine Tops Alzheimer's Prevention Study

A Shortlist of Three

An international panel of 21 dementia specialists, convened by the University of Exeter and funded by Alzheimer's Society, has identified three widely available drugs with unexpected potential against Alzheimer's disease. Published in Alzheimer's Research & Therapy, the study screened 80 existing medications and ranked the shingles vaccine Zostavax as the most promising candidate — followed by sildenafil (Viagra) and riluzole, a drug currently used to treat motor neurone disease.

Why a Shingles Vaccine?

The findings surprised many in the field. The herpes zoster (shingles) vaccine has long been used to prevent a painful rash caused by reactivation of the chickenpox virus in older adults. But a growing body of evidence suggests it may also guard against cognitive decline. Prior observational studies indicate that people who receive the jab could be roughly 16% less likely to develop dementia. A separate analysis published in Nature Medicine found that the newer recombinant version of the vaccine (Shingrix) was associated with a 17% increase in diagnosis-free time — equivalent to about 164 additional days without a dementia diagnosis.

The vaccine's appeal is practical as well as clinical. It requires a maximum of two doses, has a decades-long safety record in older adults, and is already in widespread use — meaning any protective benefit could potentially reach millions of people relatively quickly.

The Viral Connection to Alzheimer's

The biological rationale is increasingly compelling. The varicella-zoster virus — responsible for both chickenpox and shingles — can lie dormant in nerve tissue for decades before reactivating. Research shows that such reactivations trigger neuroinflammation, promote the abnormal buildup of amyloid-beta and tau proteins (hallmarks of Alzheimer's pathology), and can even reactivate herpes simplex virus type 1 in the brain. A 2025 study published in Nature, drawing on a large Welsh vaccination programme as a natural experiment, found that the shingles vaccine reduced the probability of a new dementia diagnosis by approximately one-fifth over seven years.

"Reducing subclinical and clinical reactivations of the virus may reduce reactivations of herpes simplex virus in the brain through neuroinflammatory pathways," the researchers noted — pointing to a cascade of brain damage that vaccination might interrupt.

Viagra and Riluzole Also in the Frame

Sildenafil (Viagra) placed second in the panel's ranking. Lab and animal studies suggest it protects nerve cells, improves cerebral blood flow, and reduces tau buildup. A 2025 systematic review pooling data from over 880,000 people found sildenafil use was associated with roughly a twofold reduction in Alzheimer's risk compared with non-use — a striking signal that researchers say warrants large-scale trials. Riluzole, meanwhile, showed cognitive benefits in animal models, though human evidence remains limited. Five additional drugs — including fingolimod and dasatinib — were shortlisted but did not meet the panel's priority criteria.

Next Steps: Clinical Trials Ahead

Professors Clive Ballard and Anne Corbett, who led the Exeter study, were careful to stress that none of these drugs should yet be taken preventively outside medical guidance. "These drugs need further investigation before we will know whether they can be used to treat or prevent Alzheimer's," said Corbett. The team is now planning a large UK clinical trial of the shingles vaccine using the PROTECT platform — an online brain-health registry — to test the causal relationship directly.

With over 55 million people living with dementia worldwide and approved disease-modifying therapies still scarce, the prospect of repurposing cheap, safe, already-approved drugs represents one of the most pragmatic frontiers in Alzheimer's research.