Study: Flu Shots May Reduce the Risk of Alzheimer's Disease

Getting your flu shot might have additional benefits. According to a recent study, influenza vaccination was associated with a 40% decrease in the four-year risk of developing Alzheimer's disease.

In a study conducted two years ago, the same team of researchers found a similar connection between the flu shot and a 17% reduced risk of Alzheimer's. The latest study involved a very large sample size of nearly 2 million U.S. adults aged 65 and older.

The 40% risk reduction was surprising, according to Paul Schulz, MD, a co-author of the study and director of the Neurocognitive Disorders Center at McGovern Medical School at the University of Texas Health Science Center at Houston.

“We don’t usually get to see results like that,” Schulz told Verywell. Since vaccinations usually create a mild, temporary inflammation in patients, he did not expect the flu shot to have additional benefits for a condition like Alzheimer's.

The Study

Researchers analyzed data collected from September 2009 to September 2019, which included anonymous information on medical claims from people 65 and older. The patients had no diagnosis of dementia, mild cognitive impairment, or encephalopathy at the beginning of the study.

During the follow-up period of nearly four years, around 5% of people who had received a flu shot developed Alzheimer’s disease compared with 8.5% of people who had not been vaccinated.

In the past few years, scientists have recognized that immune cells might play a role in the progression of Alzheimer's. “When we look under the microscope, we see activated immune cells around every plaque," Schulz said.

The influenza vaccine may be selectively affecting the part of the immune system that is related to Alzheimer’s, he explained. But it is too early to tell whether getting the flu shot alone can reduce the risk of developing this neurodegenerative disorder.

Heather M. Snyder, PhD, vice president of medical and scientific relations at the Alzheimer’s Association, said "more research is needed to understand the biological mechanisms behind the results in this study."

“For example, it is possible that people who are getting vaccinated also take better care of their health in other ways, and these things add up to lower risk of Alzheimer’s and other dementias," Snyder said.

Other Vaccines May Help, Too

Other vaccines may also help reduce the risk of developing Alzheimer’s, Schulz said. Adult vaccines, such as the ones against tetanus, shingles, and tuberculosis, have been associated with a lower risk of dementia.

People who received the flu shot more than once had an even lower risk of developing Alzheimer’s, as multiple vaccines may have strengthened the effect, Schulz added.

Health authorities have encouraged flu vaccinations for decades as they have a known safety profile. Even if further research fails to confirm the association between flu vaccination and risk reduction for Alzheimer's, Schulz said, people should still be getting their flu shot annually.