Seniors who got the high-dose flu shot had a nearly 55% lower Alzheimer’s risk in a study of nearly 200,000

UTHealth Houston researchers reported a nearly 55% reduction in Alzheimer’s risk among adults 65 and older who received a high-dose influenza vaccine, drawing on records for nearly 200,000 men and women. The work was published in the journal Neurology, and ScienceDaily carried the university’s release on Nov. 7. It documents an association only, and the authors stop short of saying the stronger shot prevents dementia.

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Paul E. Schulz, a neurology professor at McGovern Medical School and director of the Neurocognitive Disorders Center at UTHealth Houston Neurosciences, is the senior author. Schulz said he was stunned, as a physician, to learn that a higher-dose flu vaccine existed at all. That reaction followed a public health department’s question about dosing, and the question pushed his group to sort older adults by the strength of the shot they received instead of simply asking whether they had been vaccinated.

Two vaccine strengths and the supply gap that formed the comparison groups

The peer-reviewed paper, Risk of Alzheimer Dementia After High-Dose vs Standard-Dose Influenza Vaccination, appears in Neurology, volume 106, issue 8. Avram Samuel Bukhbinder, a McGovern Medical School graduate who is now a clinical fellow in neurology at Massachusetts General Hospital and Harvard University, is the corresponding author. The release as posted by ScienceDaily adds that the high-dose product contains four times as much influenza antigen as the standard shot, and that the CDC lists it as a preferred option for adults 65 and older.

Schulz explained how the two groups came to exist. Demand for high-dose vaccine sometimes outruns supply, so some older adults end up with the standard-dose shot instead. That substitution produced a natural split between seniors who were offered the same flu protection at different strengths, and it let the team ask whether their Alzheimer’s numbers differed. A summary from UT Physicians dated April 10 says the findings were published that day in Neurology, so the November coverage is a re-run of an earlier paper.

Supply is the detail that makes the comparison interesting. Because the shortage-driven switch to standard dose was not a choice made by the patient, the two groups may be closer in background than people who pick a stronger vaccine on their own, although the release gives no data to confirm that. If the groups are similar, the gap in Alzheimer’s diagnoses is harder to blame on who sought out the better shot, and that is the logic behind taking the finding seriously while the mechanism remains a mystery.

Reading the nearly 55% and 40% figures

The release says high-dose vaccination was linked to a nearly 55% reduction in Alzheimer’s risk, and that standard-dose vaccination was associated with a 40% reduction. The 40% number traces to earlier UTHealth Houston work on inactivated flu vaccines. Neither the release nor the News-Medical write-up states in plain terms what group the 55% is measured against. UT Physicians frames the result as high-dose compared with standard-dose, while other summaries read it as high-dose versus no vaccination, and percentages built on different baselines cannot be subtracted from one another.

The reduction was reported as stronger in women, though no sex-specific figures appear in the release.

Observational vaccine studies carry a familiar problem. People who receive a high-dose shot may differ from those who receive a standard one in income, access to care, clinic type or general health habits, and none of that is captured in a single percentage. The release says outright that the data show an association rather than cause and effect, that the biological mechanisms are unknown, and that further research is needed to learn whether high-dose vaccination itself lowers Alzheimer’s risk. It also leaves out the follow-up period, the data source and the confounder adjustments, details a reader needs from the full paper before leaning on the number.

For readers doing the arithmetic, a nearly 55% reduction corresponds to a relative risk near 0.45 for the high-dose group, but that conversion is an inference, since the release publishes no hazard ratio and no confidence interval. A wide interval could make the real effect much smaller or larger than the eye-catching percentage suggests, and the paper itself is where that range would appear.

A 2022 precursor and the scale of the disease

The group has been here before. A 2022 study led by Schulz found that flu vaccination in adults 65 and older was associated with reduced Alzheimer’s risk, and the release points to that earlier work for the 40% figure on inactivated vaccines. The new Neurology paper narrows the question from vaccinated versus unvaccinated to the dose inside the syringe, which is a smaller and more testable claim.

The stakes are large. The release cites more than 7 million Americans aged 65 and older living with Alzheimer’s in 2025, about 1 in 9 in that age group, and a projection that the number will more than double by 2050. Whether the shot itself changes dementia risk is the open question. The release calls for more research and offers no new vaccination advice beyond noting the CDC’s existing preference for high-dose products among adults 65 and older, so a senior choosing a flu shot is deciding on influenza protection alone for now.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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