There are compelling reasons to consider getting a flu shot this fall, and here’s one that may come as a surprise: it can potentially protect your brain. Recent research indicates that regular vaccinations against influenza and other infectious diseases like shingles, pneumococcal pneumonia, and tetanus, diphtheria and pertussis (whooping cough) might decrease the risk of developing Alzheimer’s disease and related dementias. “Vaccines have been a tremendous achievement in public health,” states Paul E. Schulz, a neurology professor and director of the Neurocognitive Disorders Center at the McGovern Medical School at UTHealth Houston. “They defend against a multitude of infections, many of which can be life-threatening. Now we learn that there is another enormous benefit – this time against one of the most feared diseases.”
Multiple studies have found that individuals who receive vaccinations for flu and a range of infectious diseases appear to be less likely to develop dementia compared to those who are unvaccinated. The exact reason behind this correlation is still unclear. There is a belief among some experts that infectious agents may contribute to the development of Alzheimer’s, and vaccines help by preventing or reducing the likelihood of contracting such infections.
Alternatively, Schulz speculates that vaccines may suppress an immune system response to amyloid plaque, a protein that occurs naturally but is found at abnormally high levels in Alzheimer’s. When the immune system sees plaque as a foreign invader and attacks it, chronic brain inflammation and the death of nearby neurons occur, leading to dementia. By curbing the immune response to amyloid, vaccines may save brain cells that would otherwise be killed by the immune system. Additionally, vaccines may enhance the immune system’s ability to eliminate plaque. Schulz admits that the exact mechanism is still unknown, but there is clearly a significant impact on the brain and the immune system.
Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine, concurs with the studies’ findings and states that they “suggest long-term benefits from immunizations with vaccines that may go beyond the intended direct benefits.” The precise reasons why vaccinations may slow down or prevent dementia are still uncertain. Hotez suggests that vaccines may prevent viruses from directly affecting the brain, particularly neurotropic viruses, or indirectly suppress brain inflammation caused by pathogens. Additionally, vaccines may stimulate innate immune mechanisms that could protect against the sequence of events leading to dementia.
Schulz’s recent study involved tracking two groups of participants, one vaccinated against flu and the other unvaccinated, for up to eight years. The researchers ensured that both groups shared similar characteristics, such as age, gender, doctor visits frequency, and certain medical conditions. The study found that receiving an annual flu immunization for three consecutive years reduced the risk of developing dementia by 20% over the following four to eight years. Furthermore, participants who received six flu shots experienced a 40% reduction in dementia risk. The vaccinated group had 30,000 fewer cases of dementia compared to the unvaccinated group.
Similar results were obtained in studies involving vaccines for other infectious diseases, including shingles, pneumococcal pneumonia, and the Tdap and Td combination vaccines for tetanus, diphtheria, and pertussis. For instance, when comparing vaccinated and unvaccinated patients, shingles vaccinations (both Zostavax and Shingrix) resulted in 5,311 fewer dementia cases among the vaccinated group during the eight-year follow-up. Similarly, the Tdap and Td vaccines led to 3,487 fewer dementia cases among vaccinated individuals compared to the unvaccinated group. The pneumococcal vaccine resulted in 7,975 fewer dementia cases in the vaccinated group.
Two unpublished studies conducted in the United Kingdom by researchers at Stanford University found similar outcomes. One study revealed that Zostavax vaccinations prevented around 20% of new dementia cases during a seven-year period among an older population in Wales. The other study analyzed mortality data for England and Wales over nine years and found a 5% difference in the probability of dying from dementia. Both studies used unique natural randomization to establish two comparison groups based on birth date eligibility requirements for the vaccine program.
Additional studies are needed to determine the precise effects of vaccines on the brain. Factors that are difficult to detect, such as prior head injuries, genetics, or environmental exposures, may still differentiate vaccinated and unvaccinated individuals, despite researchers’ efforts to control for them. Nevertheless, experts agree that vaccines are essential. “Vaccination, along with a good diet, exercise, intellectual and emotional stimulation are crucial factors for healthy aging,” emphasizes Hotez. Preventable diseases should not cause unnecessary suffering, states William Schaffner, a professor of preventive medicine and infectious diseases at Vanderbilt University. “Vaccinations are a critical means of staying well and living a healthy life.”
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