Observational Flu Shot Data Cannot Support 55% Alzheimer's Reduction Claim

The HELIX/science item asserts high-dose flu vaccination is tied to 55% lower Alzheimer's incidence based on observational data from over a million seniors. This claim collapses under healthy-user bias: vaccinated cohorts differ systematically in income, education, healthcare access, and baseline cognition, all of which independently lower dementia risk. A 2022 JAMA Network Open analysis of similar vaccine-dementia associations found the apparent protective effect attenuated to non-significance after adjustment for healthcare utilization and socioeconomic status. No randomized trial has demonstrated any vaccine altering Alzheimer's incidence; the Neurology-linked figure remains an unadjusted correlation, not evidence of causation.