Getting vaccinated to protect against pneumonia and flu may offer an unexpected benefit -- a lower risk of Alzheimer's disease, new research suggests.
Two new studies being presented Monday at this summer's virtual Alzheimer's Association International Conference found a lower incidence of Alzheimer's in people who got flu and pneumonia vaccines. A third study underscored the importance of prevention, reporting that people with dementia are more likely than others to die if they get serious infections.
"For people concerned about Alzheimer's disease, these vaccines may provide an extra protective effect," said Albert Amran, who is presenting his findings on flu vaccine and Alzheimer's. Amran is a medical student at McGovern Medical School at the University of Texas Health Science Center in Houston.
He and his team looked at a nationwide database of more than 9,000 people over age 60. They found that people who had received at least one flu shot had a 17% reduction in Alzheimer's disease risk. And those who consistently got their annual flu shot had an even lower risk, Amran said.
For people between ages 75 and 84, this translated to an almost 6% lower Alzheimer's risk over 16 years, the researchers noted.
Amran pointed out that the study can only show a link between vaccines and a reduced risk of Alzheimer's disease.
"Without a clinical trial, we can't say for sure that there's a causative effect," he said.
Svetlana Ukraintseva, an associate research professor at Duke University in Durham, N.C., led the second study, which examined Alzheimer's risk among more than 5,100 seniors. It found that people who got pneumonia and flu shots between 65 and 75 years of age had up to 30% lower odds of Alzheimer's.
People with genes that increase Alzheimer's risk didn't have as much of a vaccine-related reduction. This study didn't find a reduction in Alzheimer's risk based on flu shots alone.
Heather Snyder, vice president of medicine and scientific affairs at the Alzheimer's Association, said it's not yet clear how getting vaccinated might help reduce Alzheimer's risk: Does having a particular infection affect the brain somehow, setting the stage for Alzheimer's? Does getting a vaccine lead to a reduction in inflammation and other factors tied to the disease? Or, do people who get shots have healthier habits, such as exercising regularly, which can protect their brains?
"It's too early to tell," Snyder said, adding that with the emergence of COVID-19, it may be even more important to figure out. "When you look at what can contribute to your risk of Alzheimer's disease over your life course, this may be one piece of a big puzzle."
But the third study shows that preventing flu and pneumonia is vital in folks who already have dementia, because they're at far greater risk of death from serious infections.
The study, led by Janet Janbek of the Danish Dementia Research Centre at Rigshospitalet in Copenhagen, looked at roughly 1.5 million people in Denmark. It found that people with dementia who were hospitalized due to an infection had more than six times the risk of death compared to people with neither dementia nor an infection.
What's more, the risk remained higher for as much as 10 years, the study found.
Although these studies don't show a definitive cause-and-effect link between Alzheimer's disease and flu and pneumonia vaccines, Amran and Snyder said it's still a good idea to follow immunization recommendations from the U.S. Centers for Disease Control and Prevention.
The CDC recommends an annual flu shot for almost everyone 6 months of age and older. The pneumonia vaccine is typically given to people age 65 and older.
Findings presented at meetings are typically viewed as preliminary until they're published in a peer-reviewed journal.
Learn more about Alzheimer's disease prevention from the Alzheimer's Association.