• Suyeon Kim, Hwa Yeon Ko, Jeongin Oh, Dongwon Yoon, Ju Hwan Kim, Young June Choe, Ju-Young Shin, and CoVaSC Investigators.
• School of Pharmacy, Sungkyunkwan University, Suwon, Korea.
• J. Korean Med. Sci. 2025 Jan 20; 40 (3): e10e10.

BackgroundRare cases of Kawasaki disease (KD) and multisystem inflammatory syndrome in children (MIS-C) have been reported following the coronavirus disease 2019 (COVID-19) vaccination; however, the association between COVID-19 vaccination and the risk of developing KD/MIS-C has not yet been established.MethodsWe conducted a self-controlled case series analysis using a large-linked database that connects the COVID-19 immunization registry with nationwide claims data. We identified individuals aged < 18 years who received their initial COVID-19 vaccination and had a KD/MIS-C diagnosis with a prescription for intravenous immunoglobulin or corticosteroids between October 18, 2021, and April 15, 2023. The observation period was set as 240 days from the date of the COVID-19 vaccination. The risk window was 60 days after vaccination, with the remaining observation period serving as the control window. The incidence rate ratios (IRRs) and 95% confidence intervals (CIs) in the risk versus control windows were estimated using the conditional Poisson regression model. We further analyzed the vaccine doses and types for secondary analysis. We also performed subgroup analyses stratified by sex, age, comorbidities, and other conditions and sensitivity analyses by varying the length of the risk window and outcome definition.ResultsAmong 2,369,490 individuals who received the COVID-19 vaccination, 12 cases of KD/MIS-C were identified, which included five and seven patients in the risk and control windows, respectively. There was no increased risk of KD/MIS-C within the 60-day period of vaccination (IRR, 0.53; 95% CI, 0.17-1.60). Secondary subgroup and sensitivity analyses showed no significant increase in the risk of KD/MIS-C after COVID-19 vaccination, which is consistent with the results of the main analysis.ConclusionThe results of this nationwide study suggest that the risk of developing KD/MIS-C did not increase after COVID-19 vaccination. However, owing to the lack of a sufficient number of cases, future studies utilizing multinational long-term follow-up databases should be conducted. Considering the increasing incidence of KD/MIS-C and the limited understanding of its precise biological mechanisms, additional research on KD/MIS-C is warranted.© 2025 The Korean Academy of Medical Sciences.

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