Shingles vaccine tied to fewer dementia diagnoses, study in Wales suggests

Scientists may have produced the strongest evidence yet that the shingles vaccine is linked to reduced dementia risk.

Using the health records of more than 280,000 older adults in Wales, researchers found those who received the shingles vaccine were 20 per cent less likely to develop dementia over the next seven years than those who did not receive the vaccine.

The findings, published Wednesday in the journal Nature, build on other recent studies that have demonstrated associations between herpes virus infections and an increased risk of developing dementia.

Lead author Pascal Geldsetzer, from Stanford University, said the protective effects of the vaccine appeared to be "substantially larger" than those offered by existing dementia medications, but that further research was needed to determine if the observed effects were truly causal.

"If the shingles vaccine really prevents or delays dementia, then this would be a hugely important finding for clinical medicine, population health, and research into the causes of dementia," Geldsetzer said.

According to the researchers, there are two potential mechanisms that might explain how the shingles vaccine could reduce the risk of dementia, and they may even work in tandem.

The first is that vaccination reduces reactivations of dormant varicella-zoster virus, which have been shown to cause long-lasting cognitive impairment and brain pathology akin to what is seen in Alzheimer's disease.

Varicella-zoster virus, a type of herpes virus, causes chickenpox and can linger in the body for years, later reactivating as shingles.

"There is a growing body of research showing that viruses that preferentially target your nervous system and hibernate in your nervous system for much of your life may be implicated in the development of dementia."

The second possible mechanism is that vaccination triggers a more widespread immune response.

Tissa Wijeratne, a neurologist at RMIT University and Western Health who was not involved in the research, said the study was a "landmark finding" in brain health and disease prevention.

"It supports the emerging understanding that infections — especially viruses like varicella-zoster — can contribute to long-term neurological decline."

While other studies have looked at the link between shingles vaccination and dementia risk, it has been difficult for researchers to disentangle the effects of the vaccine from the effects of other variables such as diet and exercise, which can also influence dementia risk.

Randomized controlled trials are considered the gold standard for studying causal relationships and can help to eliminate these biases, but they are exceptionally expensive and resource-intensive, especially over such long periods.