An increased risk of Parkinson's disease (PD) over time may be linked to influenza infection. The effectiveness of influenza vaccination as a PD preventative intervention is yet unknown, though. Thus, this study determined if influenza vaccination in midlife (between the ages of 40 and 50) is linked to a lower risk of Parkinson's disease.
Electronic medical records from the UK's Clinical Practice Research Datalink Aurum were used in this cohort research. The study cohort was made up of people who were vaccinated against influenza between the ages of 40 and 50 between 1995 and 2017 (henceforth, with influenza immunization at midlife) and unvaccinated controls (henceforth, without influenza immunization at midlife) who were matched 1:1 in terms of age, sex, socioeconomic status, and the month of the vaccination.
Incident PD was the main result. The risk of incident PD associated with influenza vaccine at midlife vs no influenza immunization at midlife was evaluated using a modified intention-to-treat exposure definition with a 2-year lag time. Potential impact size modifiers were evaluated by secondary analyses. Sensitivity analysis investigated the effects of various possible biases.
56.6% of the 1,191,209 participants (mean age 44 ± 3 years) were women (673,920). Of these, 578,235 did not obtain an influenza vaccination during midlife, whereas 612,974 did. With crude incidence rates of 0.16 vs. 0.10 per 1000 person-years and a matched HR of 0.96 (95% CI, 0.76–1.22), midlife influenza vaccination generally did not appear to be associated with Parkinson disease risk.
Although not statistically significant, risk estimates varied over time and peaked about 8 years after immunization (HR 0.75; 95% CI, 0.52–1.08). Seasonal trends also showed up, with vaccination during flu season being associated with a lower risk estimate than off-season immunization. Sensitivity studies supported the primary findings, and age, sex, and past vaccination history had no effect on the connection.
Overall, there was no correlation between midlife influenza vaccination and the general population's risk of Parkinson's disease. Further research is needed to determine if immunization may reduce the risk of Parkinson's disease in certain patient subgroups or years following vaccination.
Source:
Douros, A., Cui, Y., Dell’Aniello, S., Suissa, S., & Brassard, P. (2025). Influenza immunization at midlife and the risk of Parkinson disease. JAMA Network Open, 8(12), e2547140. https://doi.org/10.1001/jamanetworkopen.2025.47140
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