• Jonathan Yap, Mun Yee Tham, Jalene Poh, Dorothy Toh, Cheng Leng Chan, Toon Wei Lim, Shir Lynn Lim, Yew Woon Chia, Yean Teng Lim, Jonathan Choo, Zee Pin Ding, Ling Li Foo, Simin Kuo, Yee How Lau, Annie Lee, and Khung Keong Yeo.
• Department of Cardiology, National Heart Centre Singapore, Singapore.
• Ann Acad Med Singap. 2022 Feb 1; 51 (2): 9610096-100.

IntroductionDespite reports suggesting an association between COVID-19 mRNA vaccination and pericarditis and myocarditis, detailed nationwide population-based data are sparsely available. We describe the incidence of pericarditis and myocarditis by age categories and sex after COVID-19 mRNA vaccination from a nationwide mass vaccination programme in Singapore.MethodsThe incidence of adjudicated cases of pericarditis and myocarditis following COVID-19 mRNA vaccination that were reported to the vaccine safety committee between January to July 2021 was compared with the background incidence of myocarditis in Singapore.ResultsAs of end July 2021, a total of 34 cases were reported (9 pericarditis only, 14 myocarditis only, and 11 concomitant pericarditis and myocarditis) with 7,183,889 doses of COVID-19 mRNA vaccine administered. Of the 9 cases of pericarditis only, all were male except one. The highest incidence of pericarditis was in males aged 12-19 years with an incidence of 1.11 cases per 100,000 doses. Of the 25 cases of myocarditis, 80% (20 cases) were male and the median age was 23 years (range 12-55 years) with 16 cases after the second dose. A higher-than-expected number of cases were seen in males aged 12-19 and 20-29 years, with incidence rates of 3.72 and 0.98 case per 100,000 doses, respectively.ConclusionData from the national registry in Singapore indicate an increased incidence of pericarditis and myocarditis in younger men after COVID-19 mRNA vaccination.

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