In a new retrospective cohort study, scientists at the University of Texas Health Science Center at Houston found that, through an uncertain mechanism, influenza vaccination was associated with a 40% decrease in the four-year risk of developing Alzheimer’s disease in patients 65 years or older.
The current estimate of Alzheimer’s disease prevalence in the United States exceeds 6 million people.
While some evidence suggests the incidence of dementia may be decreasing due to improvements in average cardiovascular health, the number of affected individuals is growing because of aging population.
Mounting evidence indicates that systemic immune responses can have lasting effects on the brain and can influence Alzheimer’s risk and/or progression.
A diverse range of microorganisms and infectious diseases have been associated with an increased risk and/or rate of cognitive decline, particularly among older adults, including influenzal respiratory infections, pneumonia, herpes infections, chronic periodontitis, urinary tract infections, gastrointestinal infections, sepsis, and most recently COVID-19.
Prevention or attenuation of microbe-related inflammation may therefore represent a rational strategy to delay or reduce the risk of neurodegenerative disease.
Consistent with this hypothesis, studies have found a decreased risk of dementia associated with prior exposure to various adulthood vaccinations.
“We found that flu vaccination in older adults reduces the risk of developing Alzheimer’s disease for several years,” said Dr. Avram Bukhbinder, a recent alumnus of the John P. and Katherine G. McGovern Medical School at the University of Texas Health Science Center at Houston.
“The strength of this protective effect increased with the number of years that a person received an annual flu vaccine — in other words, the rate of developing Alzheimer’s was lowest among those who consistently received the flu vaccine every year.”
“Future research should assess whether flu vaccination is also associated with the rate of symptom progression in patients who already have Alzheimer’s dementia.”
The study involved 935,887 flu-vaccinated and 935,887 flu-un-vaccinated patients.
During four-year follow-up appointments, about 5.1% of flu-vaccinated patients were found to have developed Alzheimer’s disease.
Meanwhile, 8.5% of non-vaccinated patients had developed Alzheimer’s disease during follow-up.
The results underscore the strong protective effect of the flu vaccine against Alzheimer’s disease. However, the underlying mechanisms behind this process require further study.
“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,” said Professor Paul Schulz, director of the Neurocognitive Disorders Center at the John P. and Katherine G. McGovern Medical School at the University of Texas Health Science Center at Houston.
“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.”
“Clearly, we have more to learn about how the immune system worsens or improves outcomes in this disease.”
The study was published in the Journal of Alzheimer’s Disease.
Avram S. Bukhbinder et al. Risk of Alzheimer’s Disease Following Influenza Vaccination: A Claims-Based Cohort Study Using Propensity Score Matching. Journal of Alzheimer’s Disease, published online June 13, 2022; doi: 10.3233/JAD-220361
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