Influenza vaccination is associated with a reduced Alzheimer disease (AD) risk among older U.S. adults, according to a study published online June 13 in the Journal of Alzheimer’s Disease.
Avram S. Bukhbinder, M.D., from the John P. and Katherine G. McGovern Medical School at UTHealth in Houston, and colleagues used deidentified claims data (Sept. 1, 2009, through Aug. 31, 2019) to compare the risk for incident AD between patients (aged 65 years and older) with and without prior influenza vaccination (935,887 flu-vaccinated and flu-unvaccinated matched pairs).
The researchers found that 5.1 percent of the flu-vaccinated patients and 8.5 percent of the flu-unvaccinated patients developed AD during a median follow-up of 46 months. The relative risk was 0.60 and the absolute risk reduction was 0.034, corresponding to a number needed to treat of 29.4.
“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. Instead, we believe that the immune system is complex, and some alterations, such as pneumonia, may activate it in a way that makes Alzheimer’s disease worse. But other things that activate the immune system may do so in a different way—one that protects from Alzheimer’s disease,” a coauthor said in a statement. “Clearly, we have more to learn about how the immune system worsens or improves outcomes in this disease.”