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Flu Vaccines Tied to Lower Alzheimer's Risk

More research finds an association between the annual shot and a reduced likelihood of dementia

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A flu shot may do more than keep you from getting a fever and fatigue. Accumulating research shows that the annual vaccine could pack brain health benefits as well.

Researchers from UTHealth Houston analyzed data from nearly 936,000 patients age 65 and older who received an influenza vaccine and an equal number of individuals who didn’t. They found that over a four-year period, those who had at least one flu shot were 40 percent less likely to develop Alzheimer’s disease than their unvaccinated peers.

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What’s more, the protective effect was higher among people who got the vaccine routinely. “In other words, the rate of developing Alzheimer’s was lowest among those who consistently received the flu vaccine every year,” lead study author Avram S. Bukhbinder, M.D., said in a statement. Overall, 5.1 percent of flu-vaccinated patients developed Alzheimer’s disease over the study’s four-year follow-up; the prevalence was 8.5 percent for patients who skipped the shot.

The new findings, set to be published Aug. 2 in the Journal of Alzheimer’s Disease, builds on previous research, also out of UTHealth Houston, that found having at least one flu vaccine was associated with a 17 percent reduced incidence of Alzheimer’s. Those results were presented at the 2020 Alzheimer’s Association International Conference.

How might the vaccine be connected to Alzheimer’s?

Experts have yet to identify what could be causing this association between the flu vaccine and a reduced incidence of Alzheimer’s — a disease that affects more than 6 million Americans. There are, however, a few theories. One centers on the immune system and the role it may play in the development of the brain disorder.

“Since there is evidence that several vaccines may protect from Alzheimer’s disease, we are thinking that it isn’t a specific effect of the flu vaccine,” said study coauthor Paul E. Schulz, M.D., a professor of neurocognitive disorders at the McGovern Medical School at UTHealth Houston.

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Other studies have found associations between various adulthood vaccinations — like tetanus, polio and herpes — and a decreased dementia risk. And in 2020, a team of researchers from Duke University found that adults ages 65 to 75 who were vaccinated for pneumonia had a lower prevalence of Alzheimer’s disease.

“Instead, we believe that the immune system is complex, and some alterations, such as pneumonia [a complication of flu], may activate it in a way that makes Alzheimer’s disease worse. But other things that activate the immune system may do so in a different way — one that protects from Alzheimer’s disease. Clearly, we have more to learn about how the immune system worsens or improves outcomes in this disease,” Schulz said in a statement.

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It may also be that people who keep up with their flu shots “take care of themselves in other ways” and engage in habits that are known to keep the brain healthy, Rebecca Edelmayer, director of scientific engagement at the Alzheimer’s Association, told AARP in 2020 when the findings from the first study out of UTHealth Houston were released.

Exercise, diet and sleep have all been shown to reduce risk of cognitive decline in adults. Intensive blood pressure control can also lower risks for mild cognitive impairment — a precursor to dementia.

The researchers note that future studies should look at whether flu vaccination may have an impact on the rate of symptom progression in patients who already have Alzheimer’s dementia. It’s also worth investigating whether the COVID-19 vaccines have any association with Alzheimer’s disease, they say.

Beyond dementia, the flu vaccine has been linked to lower risks for developing some cardiac events, especially for people with heart disease, according to the Centers for Disease Control and Prevention (CDC). It’s also been associated with reduced hospitalizations that arise from complications related to diabetes and chronic lung disease.

The CDC recommends that most people 6 months and older get a flu vaccine every season. This year, health officials are urging older adults to opt for a high-dose version of the shot to enhance their protection against getting seriously ill from an infection.

Editor's note: This story, originally published July 28, 2020, has been updated to reflect new information.

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