Reports of myocarditis and pericarditis following mRNA COVID-19 vaccines: A review of spontaneously reported data from the UK, Europe, and the US

Lane, S.; Shakir, S.

Background: A signal of myocarditis and pericarditis following mRNA COVID-19 vaccines first emerged in Israel in May 2021. Further cases have since been reported in multiple countries. The reporting rates of these events indicate that they are very rare given the high numbers of vaccinated persons. Males and younger vaccinees appear more frequently affected, more often following the second vaccine dose. As vaccine programmes progress with the focus shifting to younger people, it is possible that more cases of myocarditis and pericarditis will be reported. Objectives: To bring together spontaneously reported data from around the world to estimate the reporting rate in different countries and better understand the risk factors for myocarditis and pericarditis following exposure to COVID-19 mRNA vaccines. Methods: Spontaneous reports from the United Kingdom, United States, and European Economic Area were used to estimate the frequency of myocarditis and pericarditis reported following COVID-19 Vaccine Pfizer/BioNTech and COVID-19 Vaccine Moderna. Cases were stratified by age, sex, and vaccine dose where data were available. Reporting rates amongst vaccinees receiving mRNA vaccines in each region were estimated. Results: A small number of reports of myocarditis and pericarditis had been submitted to each database examined. These events are very rare according to reporting rates of spontaneous adverse reactions. The events were more frequently reported amongst males, and most reports came from vaccinees aged under 30 years. The typical clinical course of these events is mild, with full recovery in most cases. Conclusions: This study provides evidence that younger vaccinees more frequently report myocarditis and pericarditis following mRNA COVID-19 vaccines compared with older vaccinees. These very rare events with mild clinical course followed by full recovery in most cases were more frequent following the second dose. Reporting rates of myocarditis and pericarditis were consistent between the data sources.