Getting a shingles vaccination could significantly reduce the risk of dementia later in life, a study has found.
Researchers found that those who had the jab were 20 per cent less likely to develop dementia than those who didn’t.
The effect of the vaccine was far stronger in women than in men, reducing the risk for females by about 30 per cent – with the reduction for males at around 10 per cent, according to the study, by Stanford University.
It’s not clear whether the vaccine reduces the risk in its own right or if it does so by cutting the chance of getting shingles, which it is thought could play a role in dementia. It is also not known why the vaccine is more effective in women.
“Our study clearly shows that the vaccine reduces the risk of being diagnosed with dementia, and it suggests that the effect is large,” Professor Pascal Geldsetzer, of Stanford University, told i.
“Ours is the first study that uses a method that is not vulnerable to common biases in such analyses to show that shingles vaccination reduces your chance of being diagnosed with dementia.”
Previous research has suggested the shingles vaccine could reduce the risk of dementia but these are subject to clear biases, scientists say.
That’s because adults who take up the offer of a vaccine are typically more health conscious, making them less likely to develop illness such as dementia, which is at least partly caused by lifestyle factors.
But the researchers came across a dataset in Wales that has enabled them to largely remove such biases, making the results much more reliable.
It takes advantage of the fact that in a national shingles vaccination campaign across the country. In 2013, Wales determined eligibility for the jab based on an individual’s exact date of birth. Those born before 2 September 1933 were ineligible and remained ineligible for life, while those born on or after 2 September 1933 were eligible to receive the vaccine.
As a result, half of those people who were just young enough – they hadn’t quite reached their 80th birthday on the start date of the shingles vaccine programme – got the vaccine. Meanwhile, virtually no one of those who were just a little bit too old got the vaccine.
By comparing the dementia rates of the unvaccinated populations before the cutoff point with the largely-vaccinated one after it – and using a few statistical techniques – you can largely offset the other factors that could influence the result and get much closer to a cause-and-effect for the first time in regards to any protection offered by the vaccine, researchers said.
Professor Geldsetzer stressed that his research hasn’t yet been peer-reviewed and has instead been published as a ‘pre-print’ on the MedRXiv server because he was keen to speed up publication.
But he says he is “very excited to see how robust our findings are across different ways of analyzing our data and checks to examine potential biases”.
Other experts in the field, who were not involved in the study, welcomed the results.
“These are really exciting findings,” said Professor Matthew Fox, of Boston University.
“This approach allows us to get much closer to what we might expect to see if we could do a randomized trial. And the results, while they should be taken with some caution, are impressive,” he said.
A randomised trial would allocate half of the participants to have the vaccine and the other half to not at random, so that any other factors that could influence the result – such as greater health consciousness in general – could be ironed out.
Professor Fox notes that “this is a study of the effect of vaccination, not necessarily the infection itself, though the infection is the likely source.”
However, it remains unclear whether shingles can cause dementia or not.
Ivan Koychev, Consultant Neuropsychiatrist Oxford University Hospitals NHS Foundation Trust, added: “The finding is an encouraging one as it shows that vaccination against shingles can lower the risk for dementia. The excitement surrounding the study stems from its robust design.”
Professor Geldsetzer would like to see bigger, fully randomised, trials taking place to determine more precisely the effect of the vaccine.
“It is also important to bear in mind that we don’t know what the magnitude of effect on dementia prevention will be if we give the vaccine earlier in life – such as in people’s 40s or 50s – if we give the vaccine several times, such as every 5 years rather than one-off, and if we give Shingrix rather than Zostavax. Shingrix elicits a stronger and longer-lasting immune response than Zostavax, [the vaccine used in his research],” he said.