Originally published by our sister publication Infectious Disease Special Edition

By Caitie Barkley 

Prior vaccination against tetanus and diphtheria, with or without pertussis (Tdap/Td); herpes zoster (HZ); and pneumococcus are all associated with a reduced risk for developing Alzheimer’s disease, according to new research from UTHealth Houston (J Alzheimers Dis 2023 Aug 7. doi:10.3233/JAD-221231).

Researchers performed a retrospective cohort study that included patients without dementia during a two-year lookback period and were at least 65 years of age by the start of the eight-year follow-up period. They compared two similar groups of patients using propensity score matching, one vaccinated and another unvaccinated, with Tdap/Td, HZ or pneumococcal vaccine. Ultimately, they calculated the relative risk and absolute risk reduction for developing Alzheimer’s disease.

Patients who received the Tdap/Td vaccine were 30% less likely than their unvaccinated peers to develop Alzheimer’s disease (7.2% of vaccinated patients vs. 10.2% of unvaccinated patients developed the disease). Similarly, HZ vaccination was associated with a 25% reduced risk for developing Alzheimer’s disease (8.1% of vaccinated patients vs. 10.7% of unvaccinated patients). For the pneumococcal vaccine, there was an associated 27% reduced risk for developing the disease (7.92% of vaccinated patients vs. 10.9% of unvaccinated patients).

For comparison, three new anti-amyloid antibodies used to treat Alzheimer’s have shown they slow disease progression by 25%, 27% and 35%, according to Paul E. Schulz, MD, the Rick McCord Professor of Neurology at UTHealth Houston McGovern Medical School.

“We hypothesize that the reduced risk of Alzheimer’s disease associated with vaccines is likely due to a combination of mechanisms,” explained Avram Bukhbinder, MD, an alumnus of the medical school, who is now at Massachusetts General Hospital, in Boston. “Vaccines may change how the immune system responds to the buildup of toxic proteins that contribute to Alzheimer’s disease, such as by enhancing the efficiency of immune cells at clearing the toxic proteins or by ‘honing’ the immune response to these proteins so that ‘collateral damage’ to nearby healthy brain cells is decreased. Of course, these vaccines protect against infections like shingles, which can contribute to neuroinflammation.”

Alzheimer’s disease affects more than 6 million people living in the United States, with the number of affected people growing due to the nation’s aging population.

The new findings come just over a year after Dr. Schulz’s team published another study that found people who received at least one influenza vaccine were 40% less likely than their unvaccinated peers to develop Alzheimer’s disease.

“We were wondering whether the influenza finding was specific to the flu vaccine. This data revealed that several additional adult vaccines were also associated with a reduction in the risk of Alzheimer’s,” said Dr. Schulz, who is also the Umphrey Family Professor of Neurodegenerative Diseases and director of the Neurocognitive Disorders Center at McGovern Medical School. “We and others hypothesize that the immune system is responsible for causing brain cell dysfunction in Alzheimer’s. The findings suggest to us that vaccination is having a more general effect on the immune system that is reducing the risk for developing Alzheimer’s.”

Adults need a Td or Tdap booster every 10 years to maintain a high level of protection against tetanus and diphtheria. The CDC recommends adults aged 50 years and older, as well as those 19 and older who have or will have weakened immune systems because of disease or therapy, receive two doses of the zoster vaccine recombinant, adjuvanted (Shingrix, GSK). The CDC recommends pneumococcal vaccination for all children younger than 5 years of age and all adults 65 and older.

Originally published on The University of Texas Health Science Center at Houston. It has been edited for style and length.