Myocarditis and pericarditis are inflammatory conditions affecting the heart muscles and the outer lining of the heart, respectively. Patients may present with symptoms such as chest pain, shortness of breath or abnormal heartbeats. Local incidence rates remain low and the cases are usually mild and recover well. This rare risk is predominantly observed in men aged 12-29 years and largely occurs within the first week after vaccination.

Male vaccinees aged 12-29 years who are receiving any dose of Moderna/Spikevax or Pfizer-BioNTech/Comirnaty COVID-19 vaccines are advised to refrain from participating in strenuous physical activities for one week after vaccination. During this period, vaccinees should promptly seek medical attention if they experience chest pain, shortness of breath, or abnormal heartbeats.