Getting the flu shot every year can have many benefits – reducing the risk of infection and preventing hospitalizations – but new research shows the shot has another perk: reducing the risk of Alzheimer’s disease (AD).
Researchers from The University of Texas Health Science Center at Houston found that older adults who received at least one influenza vaccine were 40% less likely to develop Alzheimer’s disease over the course of four years compared to those who didn’t receive a flu shot.
Specifically, during four-year follow-up appointments, the researchers discovered that 5.1% of patients who were vaccinated against the flu developed Alzheimer’s, but 8.5% of patients who were not vaccinated developed AD during follow-up.
“It’s very surprising because most things – urinary tract infections, the flu, or broken bones – that cause inflammation accelerate AD,” Paul Schulz, MD, senior author of the study and a neurology professor with McGovern Medical School at UTHealth Houston, told Seasons. “We assumed the flu vaccination would do the same, but here we found that we don’t need to worry about the flu vaccine making AD worse; it actually reduces the risk for developing AD.”
With so many people over age 65 getting AD, the researchers could study the benefit of flu vaccination. In addition, Schulz said they chose to study the influenza vaccine because more people get this vaccine compared to others like the tetanus shot, which is only given every 10 years.
Beyond the finding that flu shots reduce the risk of AD over time, researchers also found:
- Schulz said while they’re not yet sure how long the vaccine effect will last since they only followed participants for eight years, they can say the effect appears to last for at least that duration.
- The more flu shots a person got, the more protected they were. For example, if a patient received a flu vaccine every year for eight years (the entire duration of the study), they would be considered more protected against developing AD compared to a patient who received two flu vaccines out of the eight years.
Schulz said they are now studying the effects of other vaccines to see whether they’re also protective and whether they add to the flu vaccine in terms of protection.
Why does the flu shot reduce the risk of Alzheimer’s disease?
Researchers have some theories as to why getting the flu shot can reduce the risk of AD. One theory is that the flu shot can have an impact on brain health and brain function, said Scott Kaiser, MD, a geriatrician at the Pacific Neuroscience Institute at Providence Saint John’s Health Center in Santa Monica, California.
Even if the virus does not cross directly into the brain, it can still have many impacts on cognition, he said. For example, this can be seen with long COVID and some of the symptoms that come with it such as brain fog.
“The same indirect effects of a virus on the brain could account for that,” he said.
Another theory, he added, is that when you get a vaccine, it can impact the activity of immune function—such as reducing inflammation.
“Over time as we get older, there’s this low-grade, persistent inflammation going on, including in the brain,” Kaiser said. “That may play a big role in terms of the development of Alzheimer’s disease, and potentially getting vaccinated counteracts that inflammation.”
Schulz believes the influenza vaccination actually activates the immune system in a different way that reduces the risk of Alzheimer’s.
“The different ways in which the immune system is activated by infection versus flu vaccination are very important,” he said. “However, we really don’t know how those two situations differ, resulting in such very different outcomes. If we discover how flu vaccinations help reduce the risk of AD, perhaps we could stimulate that pathway directly to reduce the risk.”
Another theory is that the influenza virus has some sequences on its surface similar to the amino acid sequence of the amyloid protein that’s at the center of amyloid plaques that lead to cell death in AD. When we vaccinate against the flu, we may be vaccinating against amyloid, Schulz said.
When should an older adult get the flu vaccine to reduce the risk of Alzheimer’s?
Because the study only looked at people over age 65, researchers couldn’t determine if vaccination prior to that is beneficial.
From an Alzheimer’s point of view, Schulz said they don’t know yet whether the specific timing of flu vaccines is important. However, it’s recommended that people get the influenza vaccine every fall before the flu season starts, as the virus is still responsible for many illnesses and deaths each year.
Schulz added more research is needed to determine whether different flu vaccines have varying effects since flu shots are formulated newly every year depending on the current strain.
“We get the flu shot annually since different strains of flu come around each year, and pharmaceutical companies modify the vaccine for the types of flu they think are most likely in any given year,” he said. “Thus, we may be able to see whether the vaccines from certain years had higher efficacies than other years.”
Proactive steps to prevent Alzheimer’s disease
- Physical exercise (for at least 150 minutes every week)
- Mental exercise (crossword puzzles, memory games, board games, reading, writing or learning something new)
- Stopping smoking
- Eating a healthy and balanced diet
- Losing weight if needed
- Consuming less alcohol
- Undergoing regular health checks with a health care provider as you get older