A flu vaccine may help reduce the risk of Alzheimer’s disease among older adults, even if they don’t get inoculated annually, a new study suggests.
The study focused on 1.87 million adults age 65 and older who had no history of dementia. Half received at least one flu vaccine over a four-year period, and half did not. During the study period, those who received the vaccine were 40 percent less likely to develop Alzheimer’s disease.
“We found that flu vaccination in older adults reduces the risk of developing Alzheimer’s disease for several years,” said the lead study author Avram Bukhbinder, MD, of Massachusetts General Hospital in Boston, in a statement.
Researchers also found that the protective effect of inoculations appeared to increase in step with the total number of annual flu shots people got during the study.
“The rate of developing Alzheimer’s was lowest among those who consistently received the flu vaccine every year,” said Dr. Bukhbinder, who did the study while at the John P. and Katherine G. McGovern Medical School at UTHealth in Houston.
How the Study Was Conducted
People in the study were matched into vaccinated and unvaccinated pairs who were similar in age and had similar medical histories, medications, and usage of healthcare visits. At the start of the study they were 74 years old on average; 57 percent of them were female.
Overall, 5.1 percent of people who received at least one flu vaccine developed Alzheimer’s disease during follow-up, compared with 8.5 percent of non-vaccinated patients, researchers reported June 13 in the Journal of Alzheimer’s Disease.
One limitation of the study is that it relied on health insurance claims data, and only included people who had benefits for both medical care and for prescription drugs. This means the findings might not apply to individuals with different types of insurance plans, the researchers noted.
While the study wasn’t designed to prove whether or how a flu vaccine might directly prevent Alzheimer’s disease, it’s possible that these inoculations trigger changes in the immune system that ward off cognitive decline, the study team suggested.
Influenza infections and other types of viral infections, including COVID-19, have also been associated with changes in the central nervous system that could contribute to cognitive decline, as a study published in June 2021 in European Archives of Psychiatry and Clinical Neuroscience found.
Other Vaccinations Are Tied to Lower Dementia Risk
Several types of vaccinations — including those for tetanus, polio, herpes, and influenza — have been linked to a decreased risk of dementia before, the study team pointed out.
An open question is whether the COVID-19 vaccine, too, might be linked to a reduced risk of Alzheimer’s disease, Bukhbinder said.
More research is needed to determine the impact of vaccinations on people who have already been diagnosed with Alzheimer’s disease.
“Future research should also assess whether flu vaccination is also associated with the rate of symptom progression in patients who already have Alzheimer’s dementia,” Bukhbinder said.