Population-Based Incidence, Severity, and Risk Factors Associated with Treated Acute-Onset COVID-19 mRNA Vaccination-Associated Hypersensitivity Reactions.

Background: COVID-19 mRNA vaccination-associated acute-onset hypersensitivity reactions have caused anxiety and may be contributing to vaccine hesitancy.

Objective: To determine the incidence, severity, and risk factors for treated acute-onset COVID-19 mRNA vaccination-associated hypersensitivity reactions in a well-characterized population.

Methods: All Kaiser Permanente Southern California (KPSC) members who received COVID-19 mRNA vaccinations between December 15, 2020, and March 11, 2021, at a KPSC facility were identified and characterized, along with all treated acute-onset vaccination-associated hypersensitivity events.