The shingles vaccine could slow the progress of dementia, according to a new study from Stanford.
These findings follow previous research that found older adults who received the vaccine were 20% less likely to develop dementia over the next seven years compared to those who didn't get the shot.
"For the first time, we now have evidence that likely shows a cause-and-effect relationship between shingles vaccination and dementia prevention and treatment," Dr. Pascal Geldsetzer, assistant professor of medicine and senior author of the new study, told Fox News Digital.
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A team of scientists used public health data in Wales, where, for several years, eligibility for the shingles vaccine (Zostavax) was based strictly on birth date.
People born just before the cutoff automatically qualified, while people born just after did not.
This created two large groups of older adults who were nearly identical in age, health profile and background, only differing by who received the vaccine. This allowed researchers to compare dementia rates in a way that avoided some of the biases seen in observational studies.
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After the initial analysis from April, researchers dug deeper into the records and found that the vaccine's benefits extended from the earliest signs of cognitive decline all the way to the last stages of dementia.
Over the course of nine years, people who received the vaccine were less likely to be diagnosed with mild cognitive impairment.
Additionally, those who received the vaccine after a dementia diagnosis were significantly less likely to die from dementia in the next nine years, suggesting that the vaccine could slow the progress of the disease.
Nearly half of the Welsh seniors who had dementia at the start of the vaccination program ended up dying from dementia in the follow-up, compared to only 30% of those who received the vaccine.
"There is a growing body of research showing that viruses that preferentially target your nervous system and hibernate in your nervous system for much of your life may be implicated in the development of dementia," said Geldsetzer.
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That includes the chickenpox virus, which stays in the body for life. In older age, it can reactivate and cause shingles, and sometimes it can trigger inflammation in or around the brain, according to Mayo Clinic.
Preventing viral flare-ups could also reduce inflammation, which has been linked to dementia risk, experts say.
The critical limitation of this research, according to the team, is that the health behaviors of those who get vaccinated are different than those who do not.
"We have very little, if any, information on these behaviors in electronic health records or medical claims data," Geldsetzer noted.
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For instance, the researchers don't know about the patients' dietary behaviors or physical activity levels.
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"If the shingles vaccine really prevents or delays dementia - and, with this new study, also appears to have benefits for those who already have dementia - then this would be a hugely important finding for clinical medicine, population health and research into the causes of dementia," Geldsetzer emphasized.
Fox News Digital reached out to shingles vaccine manufacturers for comment.
