The herpes zoster (HZ) vaccine appears to prevent or postpone dementia, according to recent data from a quasi-experiment conducted in Wales. This study examined the impact of HZ immunization on dementia incidence in a different demographic and health system environment by taking use of a comparable quasi-experiment conducted in Australia. Thus, to ascertain the impact of the HZ vaccine on the likelihood of obtaining a new dementia diagnosis, Michael Pomirchy and team carried out this investigation.
Primary care doctors in Australia began providing the live attenuated HZ vaccination to anyone aged 70–79 for free on November 1, 2016. As a result, there was a natural cutoff: those who turned 80 right before the start date were not eligible, while others who turned 80 right after were. Minimal age differences that are unlikely to be associated with health behavior are used in this quasi-experiment. With vaccination eligibility determined by birthdate, this study examined new dementia cases documented in electronic health records using regression discontinuity and birth-week data from 65 general practices.
As of November 1, 2016, the mean age of the 101,219 patients in this sample was 62.6 years, with 52.7% of them being female. People who were born just before or shortly after the date-of-birth eligibility barrier (November 2, 1936) for the HZ immunization had a well balanced history of chronic illness diagnoses and use of preventive health services.
Patients born soon before compared to shortly after the date-of-birth eligibility criterion had a sudden 16.4 percentage point increase in the likelihood of ever getting the HZ immunization. Thus, the HZ vaccination program's eligibility requirements produced comparison groups that were born close on either side of the qualifying criterion for date of birth and were probably identical to one another, with the exception of a significant variation in their likelihood of getting the intervention of interest.
This study showed that eligibility for HZ immunization reduced the likelihood of acquiring a new dementia diagnosis by 1.8 percentage points over 7.4 years. Being eligible for HZ immunization had no effect on the likelihood of seeking other preventive health care or acquiring a diagnosis of common chronic illnesses other than dementia.
Overall, compared to the current associational data, this study and the analysis conducted in Wales offer evidence that is more resilient to confounding issues (such as healthy vaccine bias).
Source:
Pomirchy, M., Bommer, C., Pradella, F., Michalik, F., Peters, R., & Geldsetzer, P. (2025). Herpes zoster vaccination and dementia occurrence. JAMA: The Journal of the American Medical Association. https://doi.org/10.1001/jama.2025.5013
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