In a study of nearly 2 million people — the largest such study to date — researchers found more evidence that flu shots help prevent Alzheimer’s and other forms of dementia.
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.
Now, according to newly published research, with two hundred times as many participants, data shows that 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.
“The strength of this protective effect increased with the number of years that a person received an annual flu vaccine,” lead author Dr. Avram 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
Could vaccines also help individuals who already have symptoms of Alzheimer’s? Schulz said more research will be needed to determine whether a flu vaccine could affect symptom progression. But we might not need to wait too long before clinical trials provide us with answers. Several companies are already developing Alzheimer’s vaccines.
Vaxxinity received the Fast Track Designation from the Food and Drug Administration for their beta-amyloid targeting vaccine, UB-311. It works by training the immune system to recognize beta-amyloid aggregates to stimulate the clearance of beta-amyloid plaques. It will commence a Phase 2b trial later this year. Other vaccine candidates, like Protollin, don’t specifically target beta-amyloid or tau proteins and instead broadly stimulate the immune system, just like the flu vaccine.