High-Dose Flu Vaccine Linked to Lower Alzheimer’s Risk in Older Adults

A flu shot may do more than protect against the flu. A study published in Neurology suggests that for adults 65 and older, the type of flu vaccine they receive may be linked to their risk of Alzheimer’s disease.

Researchers found that older adults who received a high-dose flu vaccine had a lower risk of being diagnosed with Alzheimer’s disease in the roughly two years after vaccination than those who received a standard-dose vaccine. The link was strongest in women.

Building on earlier vaccine research

Previous studies, including large studies comparing vaccinated and unvaccinated adults, have suggested that routine vaccines such as flu shots may lower the risk of Alzheimer’s disease. Until now, though, researchers hadn’t examined whether Alzheimer’s risk differs between people who receive a high-dose flu vaccine and those who receive a standard dose.

The researchers expected that adults 65 and older who got the high-dose vaccine would have a lower risk of Alzheimer’s than those who got the standard dose.

Comparing high-dose and standard-dose groups

The study used U.S. health insurance claims data from 2014 to 2019. It included adults 65 and older who had at least two years of continuous medical and pharmacy coverage and no previous signs of cognitive impairment, such as a related diagnosis or a prescription for a dementia medication.

More than 120,000 people received the high-dose vaccine, and about 44,000 received the standard dose. The average age was 73 to 74, and more than half of each group were women. Participants were followed for up to three years after vaccination.

The researchers identified new cases of Alzheimer’s disease through diagnosis codes and prescriptions for Alzheimer’s medications. They used statistical methods designed to mimic a randomized clinical trial as closely as possible, lining up each person’s start date with their vaccination and balancing the two groups on factors they could measure.

Lower risk for about 2 years after vaccination

People who received the high-dose vaccine had a significantly lower risk of Alzheimer’s disease from the first month through 25 months after vaccination.

The difference was modest. By 25 months, the researchers estimated about one fewer Alzheimer’s diagnosis for every 185 people who received the high-dose vaccine instead of the standard dose.

A stronger effect in women

When the researchers looked at men and women separately, the reduced risk was clearer in women. In women, the lower risk appeared during the first 13 months after vaccination. In men, it appeared later, between 17 and 24 months, and was significant in only one of the researchers’ analyses.

Questions researchers still need to answer

The study shows an association, not cause and effect. The researchers noted several limitations. Participants were followed for no more than three years. The claims data also didn’t include information on sociodemographic factors, lifestyle, biomarkers or deaths, all of which could affect the results.

It’s also unclear why the high-dose vaccine might be linked to lower Alzheimer’s risk. The difference could come from better protection against the flu itself, or from other effects of the vaccine that aren’t related to preventing infection. The researchers said more studies are needed to find out.

Talking with your provider about flu vaccines

Adults 65 and older who have questions about flu vaccines, including high-dose options, should talk with their health care provider about which vaccine is right for them.