mRNA COVID vaccine and myocarditis in adolescents

Comirnaty is safe and provides good antibody response, including for patients aged 12 to 15 years with clinical efficacy in protecting against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection of 100%.1 On 14 June 2021, the Food and Health Bureau, Hong Kong SAR Government lowered the age limit for receiving the Comirnaty vaccine to [greater than or equal to]12 years.2 Since April 2021, there have been reports that myocarditis and pericarditis occur more frequently in adolescents and young adults after mRNA COVID-19 vaccinations internationally.3 4 5 In Hong Kong, Comirnaty is the only mRNA technology platform COVID-19 vaccine available, but others are available elsewhere (eg, from Moderna). Myocarditis and pericarditis have many virological and immunological causes, and are known to occur after vaccination; for example, the incidence of myocarditis after smallpox vaccination is around 12 to 16.1 per million vaccinated individuals.6Myocarditis can also occur after SARS-CoV-2 infection alone or as a consequence of multisystem inflammatory syndrome in children after COVID-19 or paediatric inflammatory multisystem syndrome temporally associated with SARS-CoV-2.3 7 8 Reported cases of myocarditis after mRNA COVID-19 vaccination are mostly male adolescents and young adults aged between 12 and 24 years who received the second dose of the mRNA vaccine.9 10 11 12 13 14These heart complications are exceedingly rare, but are increasingly reported as hundreds of million doses of mRNA COVID-19 vaccines have been administered worldwide.4 5 9 10 The typical symptoms of myocarditis and pericarditis are chest pain, shortness of breath, and palpitations occurring within 1 week (usually 2-4 days) after vaccination. The Centers for Disease Control and Prevention and the Food and Health Bureau of Hong Kong SAR Government endorse the use of Comirnaty vaccine in adolescents mainly because the benefits of vaccination exceed the risks of SARS-CoV-2 infection.15 Although there is no alternative vaccine for this age-group currently available, data are being gathered on CoronaVac, which utilises the inactivated virus platform.