In persons who received both the HZV and Tdap vaccines, a significant 50% reduction in risk of dementia was seen, suggesting a nonspecific underlying association.
Vaccination against shingles (herpes zoster virus, HZV) lowered the risk for incident dementia by 25% in a study conducted by investigators at the St Louis University School of Medicine.
The retrospective cohort analysis of data from more than 200 000 individuals also found that receipt of both the HZV and Tdap (tetanus, diphtheria, pertussis) vaccinations was significantly associated with a 50% lower risk of dementia. Findings were published recently in the Journal of the American Geriatrics Society.
“Our results are consistent with prior studies of adult vaccination and lower dementia risk,” wrote authors led by Timothy Wiemken, PhD, MPH, associate professor, Division of Infectious Diseases, Allergy and Immunology. “To our knowledge, our results from VHA data provide the first evidence that receipt of two different types of vaccinations is associated with a greater reduction in dementia risk compared with receiving only Tdap or only HZ.”
The authors point to evidence from both animal and human studies supporting infectious etiology of Alzheimer disease and dementia and note that a range of vaccines, including influenza, HZ and Tdap, are associated with a reduced dementia risk. What hasn’t been well described is the dose-response relationship between vaccination and risk for cognitive decline.
Wiemken et al designed the current study to explore the potential dose response relationship between the number of different adult vaccines received and incident dementia and whether individuals who received both HZV and Tdap vaccinations had a lower risk for dementia than those who received HZV alone, Tdap alone, or neither.
For the study population, the researchers tapped deidentified medical record data from the Veterans Health Administration (VHA) (October 1, 2008–September 30, 2019) and MarketScan (January 1, 2009–December 12, 2018) for individuals aged ≥65 years. For the final analysis, after excluding ineligible files, there were 80 070 patients in the VHA sample and 129 200 in the MarketScan sample.
VHA patients were 76.8 ± 7.6 years of age, 4.4% were women, and 90.9% were White. MarketScan patients were 70.5 ± 5.9 years of age and 65.4% were women. Comorbidities were more prevalent among VHA patients, and medication use was mostly comparable between the groups.
In addition to the significant reduction of 50% in risk of dementia (95% confidence interval [CI]: 0.43–0.59) observed for study participants who received both vaccines, the investigators report reductions of 25% (HR = 0.75; 95% CI: 0.71–0.79) and 18% (HR = 0.82;95% CI: 0.76–0.89) for those who received HZV alone or Tdap alone, respectively.
Patients who received both vaccines vs only Tdap (HR = 0.61; 95% CI: 0.52–0.73) or only HZ (HR = 0.68; 95% CI: 0.58–0.79) also were significantly less likely to develop dementia.
Cumulative dementia incidence was largest in those without either vaccination (18.9% VHA, 1.9% MarketScan) and was smallest in those with both Tdap and HZ vaccination (9.1% VHA, 0.9% MarketScan).
The authors write that the results point to a nonspecific underlying mechanism that is independent of type of vaccine. “Although speculative, repeated vaccinations may train the immune system and lower the risk for chronic inflammation, increasing appropriate immune responses and the body's ability to resist bacterial and viral threats.”
“The study is important because it suggests that obtaining appropriate adult vaccinations could reduce your risk of dementia up to 50%, which is dramatically greater than any suggested other types of health behavior or risk factors,” said senior study author Jeffrey Scherrer, PhD, professor and director, Research Department of Family and Community Medicine at Saint Louis University School of Medicine, in an interview with online journal Drug Topics.
Both the recombinant zoster vaccine (Shingrix) and Tdap vaccines (Adacel, Boostrix) are on the CDC’s Recommended Adult Immunization Schedule.
Reference: Wiemken TL, Salas J, Morley JE, Hoft DF, Jacobs C, Scherrer JF. Comparison of rates of dementia among older recipients of two, one, or no vaccinations. J Am Geriatr Soc. Published online December 12, 2021. Doi:10.1111/jgs.17606