Researchers find strong evidence that shingles vaccine reduces dementia risk

Researchers have uncovered the strongest evidence yet that shingles vaccination reduces the risk of dementia, after tracking older adults in Wales.

A study comparing adults who became eligible for the Zostavax vaccine in 2013 with those who had just reached the age cut off showed a significant difference between the two groups.

The analysis of health records from more than 280,000 adults showed that those who received the shingles vaccine were 20% less likely to be diagnosed with dementia over the next seven years than those who did not have it.

It is the most conclusive finding to support the theory that viruses that affect the nervous system can increase the risk of dementia, the researchers reported in Nature.

The researchers took advantage of the fact that, in Wales, eligibility for the vaccine was determined on the basis of an individual’s exact date of birth – those born before 2 September 1933 were ineligible and remained ineligible for life, whereas those born on or after 2 September 1933 were eligible for at least one year to receive the vaccine.

Because people who were 79 when the vaccine was rolled out could have it but people who were 80 were ineligible, the study was able to remove bias relating to those who were more likely to take up an offer of a jab, the US researchers explained.

This ‘natural experiment’ meant researchers could more easily isolate the impact of being eligible for the vaccine – which makes it closer to a randomised controlled trial.

The analysis focused on people who turned 80 in the week before the introduction with those who turned 80 in the week after. About half the people who were eligible took up the offer of a vaccine, which the researchers factored into the study.

The vaccine reduced the occurrence of shingles by about 37% over seven years – a similar finding to the clinical trials.

By 2020, one in eight older adults had been diagnosed with dementia but this was 3.5 percentage points lower in those who had been vaccinated, equivalent to a 20% risk reduction.

The study also showed that protection against dementia was much more pronounced in women than in men.

Those who were eligible were not more likely to get other vaccinations or preventive treatments, nor were they less likely to be diagnosed with other common health conditions, such as diabetes, heart disease and cancer, the researchers reported.

Study leader Dr Pascal Geldsetzer, assistant professor of medicine at Stanford Medicine, said: ‘We know that if you take a thousand people at random born in one week and a thousand people at random born a week later, there shouldn’t be anything different about them on average.

‘They are similar to each other apart from this tiny difference in age. It was a really striking finding. This huge protective signal was there, any which way you looked at the data.’

Similar findings on reduced dementia risk have been reported with the new Shingrix vaccine which has been adopted in the NHS.

The shingles vaccination programme widened eligibility as well as moving to Shingrix in 2023.

Julia Dudley, head of research at Alzheimer’s Research UK, said the study strengthened the emerging link between shingles vaccination and reduced dementia risk.

She added: ‘While previous studies suggested an association, this research offers stronger evidence of a direct link, with greater benefit observed in women.

‘It’s unclear exactly how the shingles vaccine might influence dementia risk. It may reduce inflammation, support the immune system in ways that protect the brain or involve other mechanisms.

‘Understanding this link better, including the reason for any differences between men and women, could open new avenues for dementia prevention and treatment.’