Researchers from McGovern Medical School, the University of Texas Health Science Center at Houston, and colleagues at Massachusetts General Hospital in Boston sought to compare the risk for developing AD between adults with and without prior vaccination against tetanus and diphtheria, as well as with or without pertussis (Tdap/Td); herpes zoster (HZ); or pneumococcus immunizations. Results were reported in the Journal of Alzheimer’s Disease.
To determine that, the research team conducted a retrospective cohort study using Optum’s deidentified Clinformatics Data Mart Database. Patients who were free of dementia during a 2-year look-back period and were aged 65 years or older at the start of the 8-year follow-up period were included.
“We compared two similar cohorts identified using propensity score matching (PSM), one vaccinated and another unvaccinated, with Tdap/Td, HZ, or pneumococcal vaccines,” the authors explained. “We calculated the relative risk (RR) and absolute risk reduction (ARR) for developing AD.”
Results indicated that for:
• the Tdap/Td vaccine, 7.2% (n = 8,370) of vaccinated patients and 10.2% (n = 11,857) of unvaccinated patients developed AD during follow-up, with an RR of 0.70 (95% CI, 0.68-0.72) and ARR, 0.03 (95% CI, 0.02-0.03)
• the HZ vaccine, 8.1% (n = 16,106) of vaccinated patients and 10.7% (n = 21,417) of unvaccinated patients developed AD during follow-up; the RR was 0.75 (95% CI, 0.73-0.76) and ARR was 0.02 (95% CI, 0.02-0.02)
• the pneumococcal vaccine, 7.92% (n = 20,583) of vaccinated patients and 10.9% (n = 28,558) of unvaccinated patients developed AD during follow-up; the RR was 0.73 (95% CI, 0.71-0.74) and ARR was 0.02 (95% CI, 0.02-0.03).
“Several vaccinations, including Tdap/Td, HZ, and pneumococcal, are associated with a reduced risk for developing AD,” the researchers advised.
Background information in the article discussed several theories about the etiology of AD, including that infection might play a causative role in the development of AD and AD-related dementias (ADRDs). “Viral, bacterial, and fungal infections may increase neuroinflammation, thereby causing or exacerbating neurodegeneration, and subsequently dementia,” according to the study “Vaccines may reduce the risk for developing infections, or limit their severity, reducing an individual’s neuroinflammatory burden, decreasing the immune mechanisms that may contribute to the development of AD/ADRD. Alternately, vaccines may activate alternative pathways of the immune system that may alter the risk for AD/ADRD.”
Vaccinations against tetanus, diphtheria, with and without pertussis; HZ; and pneumococcus are recommended by the CDC’s Advisory Committee on Immunization Practices for older adults.
“Tetanus, diphtheria, and pertussis are bacterial infections that can lead to severe complications including hospitalization and death, especially in patients 65 and older,” study authors pointed out. “These infections are caused by Clostridium tetani through wounds, and Corynebacterium diphtheria and Bordetella pertussis through respiratory droplet. Pertussis has been of interest for researchers studying AD. One hypothesis postulates that pertussis colonization in the nasopharynx and potential accrual in the central nervous system through the olfactory nerve leads to or exacerbates amyloid-beta and tau tangle accumulation in the brain.”
“Previous studies on the effect of vaccinations on dementia risk have proven promising,” the study advises. “Recent publications utilizing a retrospective design have demonstrated a decreased risk of dementia among patients who received an HZ vaccine, Tdap vaccine or pneumococcal vaccine. However, there are gaps within the literature that this study addresses, including differences in the effects of various types of vaccines (i.e., recombinant versus live attenuated, conjugated versus unconjugated) on the risk of AD.”
The current study hypothesizes that routine adult vaccinations decrease the risk of AD in patients aged 65 years and older. Researchers also posited that the “recombinant (when compared with live attenuated) and conjugated (when compared with unconjugated) vaccinations are associated with a greater decrease in AD risk due to the stronger protection against infectious disease from Shingrix (compared to Zostavax) and the more robust adaptive immune response induced by conjugated vaccines.”
The researchers found a statistically significant association between the reduction of AD after exposure to several routinely administered adult vaccinations, including Tdap/Td (30%), HZ (25%), and pneumococcal (27%), for patients aged 65 years and older with an 8-year follow-up. “We also demonstrated that there are differences in the association of AD risk between live-attenuated (8%) and recombinant (73%) vaccinations for HZ; however, the AD risk is similar for the pneumococcal conjugate (27%) and polysaccharide (29%) vaccine types,” they added.
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