Objectives
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.

Objectives
This study analyzed the safety of coronavirus disease 2019 (COVID-19) bivalent and monovalent booster vaccines, including the frequency of adverse events (AEs) such as myocarditis and pericarditis, in adolescents aged 12 to 17 years in the Republic of Korea. We aimed to share the safety profile of the COVID-19 bivalent vaccine booster doses.
Methods
We analyzed the frequencies of AEs reported to the COVID-19 vaccination management system (CVMS) or self-reported through the text message survey (TMS). Diagnostic eligibility and causality with vaccines were compared using odds ratios (ORs) by vaccine type, and incidence rates per 100,000 person-days were calculated for confirmed cases of myocarditis and pericarditis following monovalent and bivalent booster doses.
Results
In the CVMS, the AE reporting rate (per 100,000 doses) was lower after the bivalent booster (66.5) than after the monovalent booster (264.6). Among the AEs reported for both monovalent and bivalent vaccines 98.3% were non-serious and 1.7% were serious. According to the TMS, both local and systemic AEs were reported less frequently after the bivalent vaccination than after the monovalent vaccination in adolescents aged 12 to 17 years (p<0.001). The incidence rates per 100,000 person-days for confirmed myocarditis/pericarditis following monovalent and bivalent booster doses were 0.03 and 0.05, respectively; this difference was not statistically significant (OR, 1.797; 95% confidence interval, 0.210–15.386).
Conclusion
AEs in 12- to 17-year-olds following the bivalent booster were less frequent than those following the monovalent booster in the Republic of Korea, and no major safety issues were identified. However, the reporting rates for AEs were low.