• Li Fung Peck, Wang Woon Poh, Adena Theen Lim, Sally Bee Leng Soh, Mun Yee Tham, Belinda Pei Qin Foo, Amelia Jing Jing Ng, Patricia Suet Ling Ng, Pei San Ang, Cheng Leng Chan, TohDorothy Su LinDSLHealth Products Regulation Group, Health Sciences Authority, Singapore., LeeEdmund Jon DeoonEJDDepartment of Pharmacology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore., Amelia Santosa, Bernard Yu-Hor Thong, BeverHugo VanHVDivision of Rheumatology, Immunology and Allergy, Department of Paediatrics, National University of Singapore, Singapore., Haur Yueh Lee, Chee Fang Sum, Sreemanee Raaj Dorajoo, and Desmond Chun Hwee Teo.
• Vigilance and Compliance Branch, Health Products Regulation Group, Health Sciences Authority, Singapore.
• Singapore Med J. 2024 Sep 26.

IntroductionAnaphylaxis was the first serious adverse event (AE) of special interest surfaced in Singapore following coronavirus disease 2019 (COVID-19) vaccination. Individuals who developed physician-diagnosed severe allergic reactions to the mRNA vaccines would be medically ineligible for mRNA vaccines and offered non-mRNA alternatives. This paper describes anaphylaxis reports received by the Health Sciences Authority (HSA) and presents a review of individuals who received heterologous COVID-19 vaccination.MethodsReports of anaphylaxis associated with the COVID-19 vaccines received till 31 July 2022 were reviewed and adjudicated using the Brighton Collaboration case definition criteria by an HSA-appointed expert panel. Additional review was conducted for cases with heterologous vaccination for any subsequent reactions until administration of third dose of COVID-19 vaccines.ResultsAmong 112 adjudicated anaphylaxis cases, majority occurred in females, adults and persons with allergy histories, which were consistent with global observations. Most cases (71%) occurred within 30 minutes of vaccination. The reporting incidence rates (IRs) of 0.67 and 0.55 per 100,000 administered doses for Comirnaty and Spikevax vaccines, respectively, were comparable with IRs reported overseas, whereas the IRs for non-mRNA vaccines (Sinovac-CoronaVac and Nuvaxovid) were much higher at 4.14 and 29.82 per 100,000 administered doses, respectively, likely due to selection bias. Review of the 20 cases following heterologous vaccination found varying reactions to subsequent vaccinations.ConclusionAnaphylaxis is a rare but serious AE in which outcomes can be mitigated with timely medical intervention. The case review helped to guide vaccination strategies and added to the cumulative knowledge of safety with heterologous vaccination.Copyright © 2024 Copyright: © 2024 Singapore Medical Journal.

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