Being vaccinated against shingles may also help delay getting a dementia diagnosis – a study in the journal Nature Medicine suggests.
The work builds on previous suggestions that a shingles jab may have this unintended benefit.
Researchers compared some 100,000 people who had a new shingles jab to a similar group who had an older one.
On average, those who had the new jab had an extra 164 days free from a diagnosis of dementia over six years. Further work is needed to prove the link, scientists say.
Shingles is a painful, serious condition that is more common in older people.
It is caused by a reactivation of the Herpes zoster virus – the virus that causes chicken pox.
A vaccine against shingles was introduced in many countries about 18 years ago.
Since then there has been growing evidence that the jab could help protect against dementia – but no conclusive proof.
In this study, researchers from the University of Oxford compared the health records of people in the US who had the older Zostavax jab with a newer jab, called Shingrix, which is increasingly used in the UK.
While similar numbers still got dementia by the end of the study, the researchers found, on average, over the six-year period:
- People who had Shingrix had 17% more time without a diagnosis of dementia than those who had the older vaccine
- The benefits were greater for women
Study author Prof Paul Harrison said: “Even if it is a delay of 164 days, for example, on the public health level, that would not be a trivial finding.
“It is a big enough effect that if [the link is proved] it feels meaningful to us.”
Dr Sheona Scales, at charity Alzheimer’s Research UK, said finding new ways to reduce people’s risk was “vital”.
She added: “This research, carried out in a large group of people, suggests that people given the Shingrix shingles vaccine might have a reduced risk of dementia.
“But it isn’t clear how the vaccine might be reducing risk, nor whether the vaccine causes a reduction in dementia risk directly, or whether there’s another factor at play.”
Other factors that have definitively been linked to an increased dementia risk include smoking, high blood pressure and excessive alcohol consumption, she added.
Prof Harrison said the study threw up a number of questions that need to be urgently addressed.
“One possibility is the herpes viruses may be one of the many factors that might promote dementia,” he said.
“Therefore a vaccine that is stopping you have a reactivation of the virus might delay whatever that process is that is leading you to have dementia in coming years.”
Another possibility is that ingredients in the vaccine, designed to help the body mount a protective response, could play a part, he added.
In the UK, a free shingles vaccine is available to people who turn 65, those aged between 70 and 79, and people aged 50 and over who have a severely weakened immune system.
Older shingles vaccines are now being replaced with Shingrix.
Shingrix is made by pharmaceutical company GlaxoSmithKline (GSK).
It was not involved in the research, but one of the scientists working on the study does other, separate work with GSK.
