Updated on April 7, 2025.
For more than 20 years, U.S. health officials have recommended with rare exceptions that everyone ages 6 months and older get an annual flu shot to help protect themselves and others against this seasonal virus and related complications. Since 2006, people ages 50 and older and adults ages 19 and older with weakened immune systems are also advised to get the Shingles vaccine to protect themselves against this painful rash caused by the reactivation of the varicella-zoster virus—the same virus that causes chickenpox. But recent research adds to a growing pile of evidence that these and other widely available vaccines could also help reduce the risk for Alzheimer’s disease or other forms of dementia.
One study published in April 2025 in Nature found that people who receive the shingles vaccine could be 20 percent less likely to develop dementia over the next seven years than those who are not vaccinated. The researchers were able to effectively rule out the possibility that this protective effect was due to other factors such as diet, level of education, and other lifestyle habits.
Another August 2022 study from UTHealth Houston published in the Journal of Alzheimer’s Disease, which included more than 2.3 million adults aged 65 and older, found those who got an annual flu shot were 40 percent less likely than their unvaccinated peers to develop Alzheimer’s disease within four years.
This protective effect may increase over time with consistent vaccination, according to the study’s first author, Avram S. Bukhbinder, MD. “In other words, the rate of developing Alzheimer’s was lowest among those who consistently received the flu vaccine every year,” Dr. Bukhbinder said in a news release.
Other vaccines tied to lower dementia risk
What do vaccines have to do with the brain and dementia? Scientists are still working to answer this question, but there is evidence that certain viral and bacterial infections may be linked to a higher risk for dementia.
The protective effect against dementia isn’t specific to the flu shot or the shingles vaccine. Other vaccines may also help protect against Alzheimer’s or other dementias.
For example, Alzheimer’s Disease has been linked to the oral Herpes virus (herpes simplex 1, or HSV1), certain bacteria that can cause pneumonia (Chlamydophila pneumoniae), as well as the bacteria that cause syphilis, Lyme Disease, and gum disease.
One large January 2023 study published in JAMA Network Open, which included more than 15,000 people with an average age of 55, found that those who were hospitalized with an infection were twice as likely to be diagnosed with dementia three to 20 years later, compared to those who were not hospitalized with an infection. Dementia rates were higher with infections involving the lungs, urinary tract, skin, blood, and circulatory system, as well as infections that were acquired during a hospital stay.
Another large 2021 study published in Lancet Healthy Longevity that included data from nearly one million older adults in the UK found that being diagnosed with a common infection was tied to a 53 percent higher risk for dementia within five years, compared to not being diagnosed with an infection. Risk for dementia was highest for those with sepsis, pneumonia, and hospitalization for infection.
Results from other studies have also found a link between lower risk for dementia and vaccination against shingles, pneumococcal pneumonia, tetanus, diphtheria, and pertussis (whooping cough).
How some infections may harm the brain
Scientists have a few different theories that could help explain how certain infections might increase the risk for dementia over time. Some place the blame on the virus or bacteria itself, while others think that certain infections may affect the immune system in a way that worsens this form of cognitive decline.
Some types of viruses are neurotropic. This means they can directly infect brain (nerve) cells, causing infection and harming brain tissue either right away—or even years later. For example, a type of herpes simplex virus that causes chicken pox upon initial infection can hide out in nerve cells for years, then reactivate later in life to cause painful shingles. Some scientists suggest this reactivation of dormant herpes virus may trigger a process that ultimately damages brain cells and contributes to the development of dementia.
Some infections may cause indirect damage by promoting inflammation which, in turn, harms the brain. Another more controversial theory is that the accumulation of sticky plaques (beta-amyloid proteins) in the brain, which has long been linked to Alzheimer’s disease, may be triggered by certain infections. These plaques may form to protect the brain —effectively trapping and containing harmful pathogens. Based on this hypothesis, these plaques would be similar to cholesterol in that some may be essential but high levels become dangerous.
Another reason to get vaccinated
Research into the link between infection and dementia is ongoing, but some experts suggest that routine vaccines may decrease risk for dementia by preventing infection in the first place, or by training the immune system to keep the production of amyloid plaque in check and decrease brain inflammation.
While scientists continue this investigation, one thing that is already clear: Staying up to date with routine vaccinations can help prevent potentially deadly infections and related complications. In addition to getting a seasonal flu shot each year, ask your healthcare provider about other vaccines that may be available for you, depending on your age, vaccination history, and current health status.
