Here’s What Skipping the Flu Shot Does to Your Dementia Risk

By Simon Spichak, MSc | September 20th, 2023

In a study of nearly 2 million people — the largest of its kind — researchers found more evidence that flu shots help prevent Alzheimer’s and other forms of dementia.

Have you made that free flu shot appointment at your local pharmacy yet? The data shows that people who skip their flu shot had a 60-percent higher chance of developing Alzheimer’s or other dementias than people who do get vaccinated.

The flu vaccine prevents more than 100,000 flu-related hospitalizations every year in the U.S., saving thousands of lives in the process. Flu vaccines do this by training the immune system to recognize and defeat the flu virus. More recently, scientists began to notice a surprise knock-on effect of these vaccinations: Not only do they keep the flu at bay — they appear to reduce the risk of cardiac arrest. They lower hospitalization rates for people with diabetes. And in 2020, a study presented at the Alzheimer’s Association International Conference followed more than 9,000 individuals, showing that the flu vaccine could reduce the risk of developing Alzheimer’s between 17 and 40 percent. 

According a 2022 study with two hundred times as many participants, people who do not get vaccinated against influenza have a 60-percent higher chance of developing Alzheimer’s or other dementias, compared to people who do get their flu shot.

Of course, there are all manner of variables that could influence that dramatic increase in risk, like lifestyle choices, barriers to healthcare access, and other invisible, coexisting risk factors that might go hand in hand with a person not getting a flu vaccine. Still, the numbers warrant attention, says lead author Dr. Avram Bukhbinder.

“The strength of this protective effect increased with the number of years that a person received an annual flu vaccine,” Bukhbinder said in a news release. “In other words, the rate of developing Alzheimer’s or other dementias was lowest among those who consistently received the flu vaccine every year.”

Bukhbinder conducted the research while at UT Health Houston, in collaboration with lead investigator professor Paul. E. Schulz. Their team followed more than 1.8 million cognitively-healthy older Americans, half of whom received the flu vaccine. (The study didn’t account for whether participants had the flu at the time of being tested.) After four years, 5.1 percent of vaccinated individuals and 8.5 percent of unvaccinated individuals developed dementia — a 40-percent gap. 

How vaccines might reduce the risk of Alzheimer’s

It isn’t clear why the flu vaccine resulted in such a substantial reduction in risk for developing Alzheimer’s. In the study, the authors hypothesize that the vaccine might also train the immune system to respond to beta-amyloid protein plaques — a key part of Alzheimer’s pathology. 

“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,” Schulz said

In the brain, there is a complex interplay between cells called astrocytes, microglia, and oligodendrocytes which modulates the level of inflammation. Many antibody-based drugs in development for treating Alzheimer’s stimulate the immune system to clear away beta-amyloid plaques. Similarly, the flu vaccine might just activate these immune cells in a helpful way, clearing beta-amyloid plaques, he explained.

“Some alterations, such as pneumonia, may activate it in a way that makes Alzheimer’s disease worse,” he added. “But other things that activate the immune system may do so in a different way — one that protects from Alzheimer’s disease.”

Vaccines for Alzheimer’s disease

Sure, the flu vaccine seems helpful — but could we reach a point where there are vaccines available that are designed specifically to help prevent Alzheimer’s? We might not need to wait too long before clinical trials provide us with answers. Several companies are already developing Alzheimer’s vaccines

Recently, Vaxxinity completed Phase 2b trials of its FDA-fast-tracked beta-amyloid targeting vaccine, currently known as UB-311. It’s designed to train the immune system to recognize beta-amyloid aggregates to stimulate the clearance of beta-amyloid plaques. For now, however, Phase 3 trials are yet to be confirmed.

Other vaccine candidates, like Protollin’s nasal vaccine against Alzheimer’s, don’t specifically target beta-amyloid or tau proteins and instead broadly stimulate the immune system, just like the flu vaccine.

Will one — or more — of the nine Alzheimer’s vaccines currently in the research pipeline prove safe and effective? Time will tell. In the meantime, there are vaccines out there that do seem to reduce Alzheimer’s risk.

UPDATED September 25, 2023, 01:00 A.M. ET: This July 2022 article was updated with new information about work-in-progress Alzheimer’s vaccines and other style and readability changes.

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