Flu vaccination exerts no influence on PD risk

Influenza immunization at midlife neither increases nor reduces the risk of Parkinson’s disease (PD), as shown in a study.

Researchers used electronic medical records from the Clinical Practice Research Datalink Aurum in UK. They identified 1,191,209 propensity-score matched individuals (mean age 44 years, 56.6 percent female) who were vaccinated for influenza between 40 and 50 years of age (n=612,974) and unvaccinated controls (n=578,235).

Crude incidence rates of PD did not differ between individuals who were vaccinated against influenza at midlife and nonvaccinated controls (0.16 vs 0.10 per 1000 person-years). Cox proportional hazards regression models showed no association between influenza immunization at midlife and the risk of PD (matched hazard ratio [HR], 0.96, 95 percent confidence interval [CI], 0.76–1.22).

The HR estimates varied over time, with the lowest observed approximately 8 years after vaccination (HR, 0.75, 95 percent CI, 0.52–1.08). However, the differences did not reach statistical significance.

Additionally, the HR estimates were modified by seasonality, with a lower point estimate seen among individuals vaccinated during influenza season (matched HR, 0.62, 95 percent CI, 0.33–1.15) than among those vaccinated outside of influenza season (matched HR, 1.07, 95 percent CI, 0.81–1.42).

The association between influenza immunization at midlife and PD risk did not differ in analyses stratified by age, sex, or vaccination prior to cohort entry. Sensitivity analyses supported the findings of the primary analysis.