Does the correlation between late life vaccination and reduced risk of neurodegenerative conditions such as Alzheimer’s disease exist because vaccination produces benefits such as reduced chronic inflammation via trained immunity, or because people who undergo vaccination tend to be more diligence in all matters relating to health? Mechanistic or behavioral, or both? And if both, how much of the overall observed effect size arises from each side? Researchers here find a way to obtain more insight into this correlation, as they show that different vaccine doses correlate with different degrees of reduced dementia risk. We should not expect this to be the case unless the outcome is driven by biological mechanisms resulting from vaccination.
Previous studies, including large cohort analyses comparing vaccinated and unvaccinated adults, suggest that routine immunizations such as inactivated influenza vaccines (IIVs) may reduce Alzheimer dementia (AD) risk. Whether AD risk differs after high-dose IIV (H-IIV) vs standard-dose IIV (S-IIV) remains unexamined. We hypothesized that AD risk would be lower among adults ≥65 years after H-IIV compared with S-IIV.
This retrospective cohort study analyzed data spanning 2014-2019 from IQVIA PharMetrics Plus for Academics, a US health care claims database. Eligible participants were ≥65 years with ≥2 years of continuous medical and pharmaceutical coverage and no previous diagnostic or pharmacotherapeutic indicators of cognitive impairment. Vaccinations were identified by name and Current Procedural Terminology codes. Participants were followed for up to 3 years postvaccination. Incident AD was defined using International Classification of Diseases codes and AD medication dispenses (cholinesterase inhibitors, memantine).
The H-IIV group included 120,775 unique participants (185,183 person-trials; mean age 74.4 ± 5.5 years; 57.3% female), and the S-IIV group included 44,022 participants (53,918 person-trials; mean age 73.0 ± 6.1; 56.4% female). H-IIV was associated with significantly lower AD risk during months 1-25 postvaccination. Further research is needed to clarify whether the observed difference reflects protection against influenza infection or non-infection-related mechanisms.
