Factors related to the serious adverse events in patients visiting the emergency department after ChAdOx1 and mRNA COVID-19 vaccination

Introduction: We investigated the clinical characteristics, outcomes and factors related to the serious adverse events (AEs) of patients visiting the emergency department (ED) with various AEs after ChAdOx1 and mRNA COVID-19 vaccination. Methods: Patients with AEs who visited the ED between March 2021 and September 2021 were selected from three EDs. The clinical data of these patients were collected by retrospectively reviewing medical records. Serious adverse events (AEs) were defined as any adverse medical events that led to hospital admission. Results: A total of 3572 patients visited the ED with AEs; 69.6% were administered mRNA vaccines, and the median (IQR) age was 48 (31–63) years. Regarding chief complaints, chest pain/discomfort (43.7%) was most common in the mRNA vaccines group, while fever (15.8%) was more commonly presented in the ChAdOx1 group. Most patients (93.9%) were discharged from the ED. In multivariate analysis, age ≥70 years, days from vaccination to ED visit ≥8 days, fever and dyspnea as chief complaints were higher independent risk factors for serious AEs (OR 27.94, OR 2.55, OR 1.95 and OR 2.18: p < 0.001, p < 0.001, p = 0.003 and p = 0.003, respectively). Conclusion: Most patients who visited the ED with AEs after vaccination were discharged from the ED regardless of the type of vaccine. Emergency physicians need to differentiate serious AEs and consider factors that may require admission to the ED.