New Delhi, Apr 2 (PTI) A shingles vaccine could reduce risk of dementia by a fifth, with women likely to experience a stronger protection compared to men, according to a study.
Shingles, or 'herpes-zoster', is a viral infection marked by painful rashes. It is caused by the varicella-zoster virus, which causes chickenpox. Shingles can get reactivated in the body after one has already had chickenpox. A common complication is long-term nerve pain.
Researchers, led by Stanford University's School of Medicine, US, said that the findings support an emerging theory that viruses affecting the nervous system can increase one's risk of dementia -- an ageing-related condition that progressively impairs one's cognition, including memory and thinking.
For the study, published in the journal Nature, the team looked at health records of more than 280,000 older adults in Wales (UK), aged between 71 and 88. The participants did not have dementia at the start of the shingles vaccination program in 2013.
"We show that receiving the zoster vaccine reduced the probability of a new dementia diagnosis over a follow-up period of seven years by 3.5 percentage points, corresponding to a 20 per cent relative reduction," the study quoted the authors as saying.
"This protective effect was stronger among women than men," it said.
The researchers said that while previous studies have linked shingles vaccination with a lower chance of dementia, individual differences, such as diet and exercise habits -- which differ in those vaccinated vs those not -- could not be accounted for.
Further, looking at Wales' national health records, the researchers could analyse the effect of being eligible for the vaccination by comparing people who turned 80 just before September 1, 2013, with people who turned 80 just after.
While the rules were designed to ration the limited supply of the vaccine, they also meant that the slight difference in age between 79- and 80-year-olds made all the difference in who had access to the vaccine, the researchers said.
The circumstances, well-documented in the country's health records, were about as close to a randomised controlled trial (considered the gold standard of clinical trials) as you could get without conducting one, according to senior author Pascal Geldsetzer, assistant professor of medicine, Stanford University.
Over a follow-up period of seven years, the researchers compared the health outcomes of people eligible and ineligible for the vaccine, all of whom were roughly the same age.
The team found that the vaccine reduced the occurrence of shingles by about 37 per cent, similar to what had been found in clinical trials of the vaccine.
The researchers also found that by 2020, one in eight older adults -- aged 86 and 87 by this time -- had been diagnosed with dementia.
However, those inoculated with the shingles vaccine were 20 per cent less likely to develop dementia, compared to the unvaccinated.
"It was really a striking finding. This huge protective signal was there, which way you looked at the data," Geldsetzer said.
The study also found that the protection against dementia was much more pronounced among women than men.
This could be due to sex-related differences in immune response or in the way dementia develops, Geldsetzer said.
For example, women on average have a higher antibody response to vaccination and shingles is more common in women, compared to men, the researchers said.
They added that if the results are confirmed in future studies, shingles vaccination could present as a preventive intervention for dementia.
Reacting to the findings, Vinod Balasubramaniam, associate professor from Monash University, Malaysia, said the study presents "compelling evidence".
"The findings align with evidence implicating varicella-zoster virus (VZV) reactivation in neurodegenerative processes, potentially through neuroinflammation. The potential implications are substantial," said Balasubramaniam, not involved in the study.
"Should causality be established, this widely available vaccine could serve as a cost-effective tool to mitigate dementia, a global health challenge impacting millions and imposing significant economic burdens," Balasubramaniam said.
He added that the study's results could bolster vaccination uptake and help form public health strategies.