Flu and pneumonia vaccines were associated with a lower risk of developing Alzheimer's disease among thousands of adults over age 60, according to two new studies presented Monday at the Alzheimer's Association International Conference.
The studies haven't been published.
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Can vaccinations reduce Alzheimer's risk?
For one of the studies, researchers at the University of Texas analyzed millions of patients' medical records with the goal of identifying factors that affected peoples' risk of developing certain diseases, including Alzheimer's.
According to Albert Amran, an author of the study and medical student at McGovern Medical School at the University of Texas Health Science Center, the researchers identified one surprising association: receiving a flu shot was associated with a lower risk of developing Alzheimer's.
Because the association was particularly unexpected, according to Amran, the researchers did a deeper analysis of the medical records of about 9,000 people ages 60 and older, including some who had received flu shots and some who didn't. The researchers tried to control for other known risk factors for Alzheimer's in their analysis. "We [tried] to make sure that both groups had an equal amount of, say, smoking status, obesity, diabetes, cardiovascular disease," Amran explained.
The team also considered risk factors such education and income, as well as the number of prescriptions the patients involved in the analysis were taking. They researchers tried to ensure that the sample of patients who had received flu vaccines weren't generally healthier than the participants who weren't vaccinated against the flu.
Even after implementing controls for all of those factors, the researchers still found that receiving at least one flu shot was associated with a 17% reduction in Alzheimer's risk when compared with those who weren't vaccinated, Amran said. Receiving regular flu vaccinations was associated with an additional 13% decrease in Alzheimer's risk, the researchers found.
For the other study presented Monday, a separate team of researchers from Duke University and the University of North Carolina analyzed the medical records of more than 5,000 people who were age 65 or older and found that receiving a pneumonia vaccine between ages 65 and 75 was associated with a reduction of at least 25% in the patients of developing Alzheimer's when compared with patients who didn't receive the vaccination during that period in their lives. In some patients, receiving a pneumonia vaccine between ages 65 and 75 was associated with a reduction in Alzheimer's risk of up to 40%, the researchers found.
Svetlana Ukraintseva, an associate research professor in the Biodemography of Aging Research Unit at Duke's Social Science Research Institute who was involved with the study, said she and her colleagues did not identify any additional reductions in Alzheimer's risk among patients who received the flu vaccine.
What do the findings mean?
Paul Schulz, director of the neurocognitive disorders center at McGovern, said the results were "the opposite of what any[one] … thought," because vaccines usually cause inflammation—which can contribute to Alzheimer's disease risk.
According to Arman, the studies' results indicate that "[m]ore vaccinations meant less Alzheimer's." However, he warned that researchers don't know why vaccinations appear to be beneficial when it comes to Alzheimer's risk, and he explained that potential benefits from vaccines could vary among different groups of patients.
"There is a protective effect," Arman said, but "[h]ow much is something that needs to be quantified with a more intensive study."
Ukraintseva said the vaccines could "improve immunity on a broad scale," which can result in "beneficial off-target effects on health that span beyond the protection against specific disease."
For instance, Maria Carrillo, chief science officer of the Alzheimer's Association, explained that the vaccines could protect against Alzheimer's because the flu and pneumonia can sometimes affect the brain, which could increase Alzheimer's risk. "Every time you have one of these infections you may experience a challenge to your memory and thinking," Carrillo said.
Ultimately, Carrillo said, "[w]e've always known that vaccines are very important to our overall health," adding, "[a]nd maybe they even contribute to protecting our memory, our cognition, our brain" (Hamilton, NPR, 7/27; George, Medpage Today, 7/27; Alzheimer's Association International release, 7/27).