According to a Claims-Based Cohort Study, people who received at least one influenza vaccination were 40% less likely compared to their non-vaccinated peers to develop Alzheimer's disease (AD).  Utilizing deidentified claims data, investigators intended to assess the occurrence risk of AD between individuals who had prior influenza vaccine and those who had not in a large US claims database.

Study participants had no dementia during the 6-year look-back period and were >65 years old when the study began. Cohorts of flu-vaccinated and flu-unvaccinated people with identical baseline demographics, comorbidities, medication use were established by propensity-score matching (PSM). During 4-year follow-up, absolute risk reduction (ARR) and relative risk (RR) were used to evaluate effects of influenza vaccine on AD.

From an unmatched sample of eligible participants (n = 2,356,479), PSM generated a sample of 935,887 flu-vaccinated-unvaccinated matched pairings. The matched group (56.9% were female) was 73.7 years of age, with a median follow-up of 46 months. During follow-up, 5.1% (n = 47,889) of flu-vaccinated patients and 8.5% (n = 79,630) of the flu-unvaccinated patients had AD. The RR was 0.60 and the ARR was 0.034, resulting in a number needed to treat of 29.4. Hence, influenza vaccination was associated with minimized risk of incident AD in older adults aged 65 years and older.