Objective: Urticaria is a mast cell-related disease caused severe itching and the lifetime prevalence of urticaria is about 20% in general population. Our purpose is to evaluate risk of urticaria in geriatric stroke patients received influenza vaccination (IV). Methods: In a cohort of 192,728 patients with newly diagnosed stroke aged over 65 years obtained from 23 million people in Taiwan’s National Health Insurance between 2000 and 2008, we identified 9890 stroke patients who received IV and 9890 propensity score-matched stroke patients who did not receive IV. Controlling for immortal time bias, both the IV and non-IV groups were followed for one year. Urticaria events were identified during the follow-up period. We calculated the adjusted rate ratios (RRs) and 95% confidence intervals (CIs) of the one-year risk of urticaria associated with IV. Results: During the follow-up period of one year, stroke patients with IV had a significantly higher risk of urticaria compared with non-IV stroke patients (RR 1.81, 95% CI 1.47–2.23). An increased risk of urticaria in stroke patients with IV was noted in both sexes, patients 65–84 years of age, patients with comorbid medical conditions, and various time intervals of follow-up. Vaccinated stroke patients with hemorrhage (RR 4.00, 95% CI 1.76–9.10) and those who received intensive care (RR 5.14, 95% CI 2.32–11.4) had a very high risk of urticaria compared with those without IV. Conclusion: Receiving IV may be associated with an increased risk of urticaria in stroke patients. We could not infer the causality from the current results because of this study’s limitations. Future investigations are needed to evaluate the possible mechanism underlying the association between IV and urticaria.
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