Shingles Vaccine and Alzheimer's: New Evidence Suggests Protection May Extend Well Beyond Shingles Itself

A study published in the journal Cell on December 2, 2025, led by researchers at Stanford University, has added significant new evidence to a growing body of research suggesting that the herpes zoster vaccine, commonly known as the shingles vaccine, may have meaningful protective effects against dementia beyond its intended purpose of preventing shingles infections.

The new study is a follow-up to an earlier investigation published in Nature in early 2025, which found that Welsh adults who received the shingles vaccine were approximately 20 percent less likely to receive a new dementia diagnosis over the following seven years compared to adults who were not vaccinated. The strength of that finding was amplified by the study's design: a natural experiment in Wales where shingles vaccine eligibility was assigned based on exact date of birth at the programme's launch in September 2013. This created two groups that differed in almost no respect except vaccination status, producing evidence that researchers describe as approaching causal strength rather than simple correlation.

The December 2025 Cell study analysed the same Welsh cohort of more than 282,500 adults but asked a different question: does the vaccine affect dementia in people who already have a diagnosis? The results were striking. Among the 7,049 Welsh seniors who had already been diagnosed with dementia at the start of the vaccination programme, nearly half died from dementia during the follow-up period. Among those who received the vaccine, only about 30 percent died from dementia. The findings were confirmed using a separate Australian cohort with a similar shingles vaccination programme structure. The protective effect was more pronounced in women than in men.

The biological explanation being explored centres on the varicella-zoster virus (VZV), which remains dormant in nerve cells for life after a primary chickenpox infection. Research has linked VZV reactivation to amyloid deposition and aggregation of tau proteins, both hallmarks of Alzheimer's pathology, as well as to cerebrovascular patterns resembling those found in Alzheimer's disease. Subclinical VZV reactivations may act as a chronic immune stressor that accelerates neuroinflammation and cognitive decline over time.

The study's senior author, Dr Pascal Geldsetzer of Stanford, described the therapeutic finding as the most exciting part of the research. The implication that a widely available vaccine could slow the progression of dementia in people who already have the disease represents a fundamentally different category of intervention. Current approved therapies for dementia have shown limited and modest clinical benefits. A shingles vaccine, already recommended for adults 50 and older, widely available, and supported by a strong safety record, could be reframed as a tool for slowing dementia progression at scale.

Important caveats apply. This is observational evidence from a natural experiment, not a randomised controlled trial specifically designed to assess dementia outcomes. Experts including Alberto Ascherio of Harvard's T.H. Chan School of Public Health have called the findings promising while stressing that additional dedicated prospective studies are needed to confirm the benefit.

Sources: Cell (December 2, 2025, DOI: 10.1016/j.cell.2025.11.007) | Nature (2025, DOI: 10.1038/s41586-025-08800-x) | Stanford Medicine News | CNN Health | Harvard T.H. Chan School of Public Health | Fisher Center for Alzheimer's Research Foundation