Serious Adverse Reactions to COVID-19 vaccines in Portugal up to July 2021: thrombosis with thrombocytopenia syndrome, myocarditis/pericarditis, and Guillain-Barré syndrome

Serious adverse reactions to COVID-19 vaccines may be related to death or other serious clinical events. The aim of this study was to describe and to analyze the profile of serious notified Adverse Drug Reactions (ADRs) and the occurrence of some rare and serious adverse reactions to COVID-19 vaccines in Portugal up to 22 July 2021. Data was collected from public reports of INFARMED, I.P. (the Portuguese medicine agency). Up to 22 July 2021, there were 11,002,983 administered COVID-19 vaccines in Portugal, with 11,314 notified ADRs: 36% serious and 64% non-serious. Overall, 1 ADR and 0.4 serious ADRs were reported per each 1,000 administered vaccines, respectively. There were 2 confirmed cases of thrombosis with thrombocytopenia syndrome (TTS), 3 probable cases of Guillain-Barré syndrome (GBS), and 2 definitive cases of myocarditis/pericarditis, among the studied rare serious ADRs. In conclusion, as expected, rare cases of TTS, GBS and myocarditis/pericarditis were reported, which contribute to the maintenance of a safety profile of COVID-19 vaccines at national and international levels. Keywords: COVID-19 vaccines; thrombosis with thrombocytopenia syndrome; Guillain-Barré syndrome; myocarditis; pericarditis