Incidence and Risk Factors of Immediate Hypersensitivity Reactions and Immunisation Stress-related Responses with COVID-19 mRNA Vaccine

Background With the implementation of mass vaccination campaigns against COVID-19, the safety of vaccine needs to be evaluated. Objective We aimed to assess the incidence and risk factors for immediate hypersensitivity reactions (IHSR) and immunisation stress-related responses (ISRR) with the Moderna COVID-19 vaccine. Methods This nested case-control study included recipients who received the Moderna vaccine at a mass vaccination centre, Japan. Recipients with IHSR and ISRR were designated as cases 1 and 2, respectively. Controls 1 and 2 were selected from recipients without IHSR or ISRR and matched (1:4) with cases 1 and cases 2, respectively. Conditional logistic regression analysis was used to identify risk factors associated with IHSR and ISRR. Results Of the 614,151 vaccine recipients who received 1,201,688 vaccine doses, 306 recipients (cases 1) and 2,478 recipients (cases 2) showed 318 events of IHSR and 2,558 events of ISRR, respectively. The incidence rates per million doses were estimated as – IHSR: 266 cases, ISRR: 2,129 cases, anaphylaxis: 2 cases, and vasovagal syncope: 72 cases. Risk factors associated with IHSR included female, asthma, atopic dermatitis, thyroid diseases, and history of allergy; for ISRR, they were younger age, female, asthma, thyroid diseases, mental disorders, and a history of allergy and vasovagal reflex. Conclusion In the mass vaccination settings, the Moderna vaccine can be used safely owing to the low incidence rates of IHSR and anaphylaxis. However, providers should beware of the occurrence of ISRR. Risk factor identification may contribute to the stratification of high-risk recipients for IHSR and ISRR.