A recent study published in Neurology found that adults aged 65 and older who received a high-dose influenza vaccine had a lower risk of developing Alzheimer's dementia compared to those who received the standard-dose version, according to an Apr. 2 report. The association was particularly strong among women, raising questions about whether stronger immune responses from vaccines could help protect the aging brain.
The findings are significant as they build on previous research suggesting routine vaccination may reduce the risk of Alzheimer's disease (AD) in older adults. Some earlier studies have shown up to a 40% reduction in dementia incidence over four years among vaccinated individuals, but it was unclear if enhanced formulations like high-dose vaccines offered greater protection than standard doses.
Researchers analyzed data from the IQVIA PharMetrics Plus for Academics database covering August 2014 through July 2019. The study included individuals with at least two years of continuous insurance coverage and no prior signs or treatments for cognitive impairment or dementia. Vaccination status was determined using administrative claims, and new cases of AD were identified by diagnostic codes or prescriptions for US Food and Drug Administration-approved symptomatic treatments.
To strengthen their analysis, researchers used target trial emulation across multiple cohorts and applied statistical weighting methods to balance baseline characteristics between groups. They estimated both per-protocol and intention-to-treat effects, adjusting for factors such as demographics, comorbidities, medication use, and healthcare utilization.
The high-dose group included more than 120,000 people with an average age of 74; the standard-dose group included over 44,000 people with an average age of 73. Follow-up periods averaged between 14-19 months depending on analysis type. Results showed that high-dose vaccination was associated with a significantly lower risk of incident Alzheimer's dementia—particularly during the first two years after vaccination—with benefits more pronounced among women.
While sensitivity analyses supported these primary findings even under stricter definitions or lagged follow-up periods, secondary analyses regarding mild cognitive impairment produced mixed results. The authors cautioned that limitations such as short follow-up timeframes and reliance on claims-based diagnoses mean results should be interpreted carefully.
Researchers concluded that further prospective studies are needed to confirm these associations in broader populations using biomarker-confirmed outcomes. They also noted that because this was not a randomized controlled trial but rather an observational analysis based on insurance claims data, causality cannot be definitively established.
