Safety of the bivalent COVID-19 mRNA booster vaccination among persons aged over 18 years in the Republic of Korea.

Background: The aim of this study was to disseminate information about the safety of bivalent coronavirus disease 2019 (COVID-19) mRNA booster vaccines administered to adults in the Republic of Korea.

Methods: Two databases were used to assess the safety of COVID-19 booster doses of Pfizer BA.1, Pfizer BA.4/5, Moderna BA.1, and Moderna BA.4/5 vaccines for adults aged 18 years and older. Adverse events (AEs) were analyzed using data reported to the web-based COVID-19 vaccination management system (CVMS) and a self-reported text-message survey.

Results: Between October 11, 2022 and March 30, 2023, the CVMS received reports of 2,369 (93.7%) non-serious AEs from vaccinated adults, along with 158 (6.3%) serious AEs, which included 5 cases of anaphylaxis and 33 deaths. From October 11, 2022 to January 27, 2023, 40,022 people aged 18 and older responded to a survey conducted via text message. The booster doses were associated with fewer local and systemic AEs compared to the original vaccines. After receiving the bivalent vaccine, the most commonly reported AEs were pain at the injection site, headache, fatigue, and myalgia.

Conclusion: Overall, bivalent vaccines exhibited fewer AEs compared to the original vaccines. The majority of AEs were non-serious, and serious AEs were rare among adults aged 18 years and older following vaccination with the Pfizer and Moderna bivalent vaccines.