High-dose flu vaccine linked to lower risk of Alzheimer’s disease

• Among people aged 65 and older, the high-dose flu vaccine was associated with an almost 55% lower risk of Alzheimer’s disease
• For the standard dose, researchers reported a 40% reduction in risk
• The results show an association, but do not prove that vaccination prevents the disease

What the study found

Researchers at UTHealth Houston examined whether a dose of the annual flu vaccine was associated with the likelihood of developing Alzheimer’s disease in people over 65. The analysis included data from nearly 200,000 men and women. Those who received a vaccine with a high dose of antigen had a lower risk of the disease than those who received a standard dose. The study was published in the medical journal Neurology and builds on the team’s research into a possible link between vaccination and brain health.

The importance of this question is tied to the scale of the disease among older Americans. According to figures cited in the publication, more than seven million U.S. residents aged 65 and older were living with Alzheimer’s disease in 2025—about one in nine people in this age group. By 2050, that figure is expected to more than double, according to the cited estimate. Alzheimer’s is the leading cause of dementia, so possible links between routine vaccinations and disease risk are drawing researchers’ attention.

The new study builds on 2022 research in which a team led by neurologist Paul Schulz found an association between flu vaccination and a lower risk of Alzheimer’s disease in people aged 65 and older. Later, local public health officials invited Schulz to discuss the earlier findings and asked whether different doses might matter. This led to a more specific question: Is a stronger vaccine associated with an additional reduction in risk? The new study examined this association specifically.

Why compare vaccine doses

As people age, their immune systems gradually become less effective at recognizing and fighting infections. As a result, the flu can be especially dangerous for older adults. The CDC recommends a high-dose vaccine as the preferred option for people aged 65 and older, designed to produce a stronger immune response. This recommendation addresses age-related vulnerability; it does not mean the vaccine guarantees protection against the flu or Alzheimer’s disease. The researchers separately examined whether the dose was associated with the latter condition.

The high-dose vaccine contains four times as much influenza antigen as the standard vaccine. Antigens are components of a vaccine that help the immune system recognize the virus and prepare a defense. Until 2022, the CDC did not identify one type of flu shot as preferable for people over 65; the main message was to get vaccinated every year, regardless of the formulation. These distinctions matter in the study because it compares two vaccine doses—not vaccinated and unvaccinated people.

The availability of vaccines also provided a practical reason to compare doses: demand for high-dose vaccines sometimes exceeds supply, so some older adults receive the standard version. This allowed researchers to compare outcomes among people who received different vaccine formulations. The team was able to gather data on thousands of older adults and then analyzed nearly 200,000 participants aged 65 and older. Age itself is associated with an increased risk of Alzheimer’s, making this group particularly relevant for such a comparison.

How to interpret the results

The analysis included men and women aged 65 or older who received either a high-dose or standard-dose flu vaccine. The study’s main finding was a difference in the statistically observed risk of Alzheimer’s disease between the groups: the risk was lower among those who received the high dose. The published description does not provide further details about the follow-up period or how the groups were formed, so these findings should be described within the limits of the data presented, without attributing unspecified characteristics to the study.

The authors reported that standard-dose vaccination was associated with a 40% lower risk of Alzheimer’s disease, while the high dose was associated with a reduction of nearly 55%. These figures describe the reduction in risk reported by the researchers and should not automatically be interpreted as a promise of the same effect for every person. In addition, the comparison does not mean that the high dose reduces risk by exactly 15 percentage points relative to the standard dose: the source provides estimates for both groups, but not that direct calculation.

The association with lower risk was especially pronounced among women: according to the study’s findings, they appeared to have a greater reduction in risk with the high dose. This observation reflects the analysis results and does not establish why the difference appeared in this way. The source does not report separate numerical estimates for women and men, so the size of this difference cannot be specified. In practical terms, the finding points to a direction for further study, not to an individual prediction for a particular woman or man.

What remains unknown

A key limitation of the finding is that the study identified an association, rather than proving a causal relationship. We cannot conclude that the high-dose vaccine itself prevents Alzheimer’s disease: the observed difference may warrant further investigation, but on its own it does not confirm a mechanism of action. The authors note that the results add evidence to a possible link between flu vaccination and brain health. Whether the immune response could affect processes associated with the disease remains an open question.

The new research also does not erase the distinction between preventing flu and preventing dementia. Annual vaccination is generally recommended, and flu and its complications are especially dangerous for people already living with cognitive impairment. For people over 65, the CDC recommends a high-dose vaccine as the preferred option, but the Alzheimer’s study does not establish a separate medical recommendation based on proven prevention of the disease. The source emphasizes the need for further research.

Further research is needed to assess the significance of the findings: the available data do not answer whether vaccine dosage directly affects the development of Alzheimer’s disease. It is also unclear what biological processes might explain the observed association. For now, the only reliable takeaway is that the analysis covered nearly 200,000 people over 65 and found a stronger association with the high-dose vaccine. The findings do not justify promising protection against Alzheimer’s or making individual predictions based on vaccine type.

Source: ScienceDaily