GSK Plc’s shingles vaccine was linked to a longer delay in dementia onset than a competing shot, a finding that suggests superior protective powers against one of the world’s most threatening conditions.

People who received the Shingrix vaccine lived an average of 164 days longer without a dementia diagnosis than those who got Merck & Co.’s Zostavax, according to a study published Thursday in the Nature Medicine journal. The Merck vaccine was linked to lower dementia risk in a study last year.

More than 55 million people worldwide have dementia, the seventh leading cause of death among older people globally. While recently approved drugs like Eisai Co.’s Leqembi and Kisunla from Eli Lilly & Co. can help slow the progress of Alzheimer’s disease—one of the most common dementia forms—there is no cure.

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“The next question is how does vaccination exert this dementia protection effect?” said Rob Howard, a professor of old age psychiatry at University College London who wasn’t involved in the study. It could be through reducing levels of the virus, or by affecting some mechanism of the disease itself, he said.

The study, conducted by scientists at the University of Oxford, included data from more than 200,000 people in the U.S. who had received one of the shots over the past decade. About half received Zostavax between October 2014 and September 2017, while others received Shingrix between November 2017 and October 2020. Zostavax, a live vaccine, has been largely discontinued in the U.S. in favor of Shingrix, a recombinant shot.

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The researchers followed subjects for six years after they received shots, comparing the prevalence of dementia diagnoses in both groups. The Shingrix shot delayed dementia longer in women than men. An earlier study of Zostavax found little impact on dementia in men at all.

The efficacy appears to be comparable to that seen in the new drugs for Alzheimer’s, said Andrew Doig, a professor of biochemistry at the University of Manchester. More studies might show whether there’s benefit in giving the shingles vaccine at younger ages, he said.

The findings should prompt further research about how exactly the protection could arise and should be confirmed in a large-scale, randomized control trial, the authors wrote.