High-Dose Flu Shot Tied to Nearly 55% Lower Alzheimer’s Risk in Seniors
Adults 65 and older who got a high-dose flu shot had a nearly 55% lower Alzheimer's risk in a Neurology study. What it found and what it can't show.
Older adults who received a high-dose flu vaccine had a nearly 55% lower risk of developing Alzheimer’s disease, according to a study of nearly 200,000 people ages 65 and older published in the journal Neurology. Researchers at UTHealth Houston compared that with a 40% reduction they had previously tied to the standard-dose shot.
The study shows an association, not cause and effect. The authors say more research is needed before anyone can conclude that a stronger flu shot protects the brain.
How the researchers compared the two shots
The team used health data on men and women 65 and older and compared Alzheimer’s diagnoses in two groups: people who got the high-dose flu vaccine and people who got the standard dose. This is an observational analysis of existing records. Nobody was randomly assigned to one vaccine or the other.
The comparison was possible because supply of the high-dose vaccine sometimes falls short of demand, so some seniors end up with the standard version. “We were able to put together thousands and thousands of people,” said Paul Schulz, the study’s senior author and a professor of neurology at McGovern Medical School at UTHealth Houston.
High-dose flu vaccines carry four times as much antigen as standard shots. An antigen is the part of a vaccine that trains the immune system to recognize a virus. Immune defenses weaken with age, and the extra antigen is meant to produce a stronger response in older people. The Centers for Disease Control and Prevention lists high-dose vaccines as a preferred option for adults 65 and older. Before 2022, the agency did not favor one injectable flu vaccine over another for that age group.
What the study found
People in the high-dose group were significantly less likely to develop Alzheimer’s than those in the standard-dose group, the researchers reported. The difference was larger in women, who appeared to gain more from the stronger shot.
The work builds on a 2022 study by Schulz’s team, which found that flu vaccination in general was associated with lower Alzheimer’s risk in adults 65 and older. Earlier UTHealth Houston research had linked inactivated flu vaccines, made with viruses that cannot cause infection, to a 40% lower risk.
The new question came from an unexpected place. Local public health officials who had read the earlier research asked Schulz whether the vaccine dose made a difference. He said he had not known a higher dose was available. “I was stunned,” he said.
What is still unclear
Because the study is observational, it cannot rule out other differences between the two groups that might explain part of the gap. The researchers say further studies are needed to test whether high-dose vaccination itself lowers Alzheimer’s risk and, if so, how. One possibility they raise is that the immune response set off by vaccination affects biological processes involved in the disease, but that has not been shown.
The paper, “Risk of Alzheimer Dementia After High-Dose vs Standard-Dose Influenza Vaccination,” appears in Neurology, volume 106, issue 8 (DOI: 10.1212/WNL.0000000000214782). Avram Samuel Bukhbinder, a clinical fellow in neurology at Massachusetts General Hospital and Harvard University, is a corresponding author. Researchers from UTHealth Houston’s McWilliams School of Biomedical Informatics also took part.
Why it matters
Alzheimer’s is the leading cause of dementia. In 2025, more than 7 million Americans 65 and older were living with it, about 1 in 9 people in that age group, and that number is projected to more than double by 2050.
Researchers are looking for practical ways to lower that risk, and flu shots are already widely given, with high-dose versions made specifically for older adults. The findings suggest vaccine dose should be tracked in future studies of the immune system and Alzheimer’s. Preventing the flu itself also matters for people who already have Alzheimer’s, since infection and its complications carry serious risks for people with cognitive impairment.
Source: ScienceDaily
