Myocarditis and Pericarditis after Administration of an mRNA Covid-19 vaccination

By Dr Rohit Khurana

Recently, we've seen several patients, mostly teenagers and young men, coming in several days after a dose of the Pfizer or Moderna vaccine. These individuals come in with symptoms like chest discomfort, laboured breathing and palpitations.

Naturally, media reports of complications create a fear of developing pericarditis and myocarditis. The question of safety for the 2nd vaccine dose is a concern if the symptoms have occurred after the 1st dose.

Myocarditis is inflammation of the muscle of the heart. Pericarditis is inflammation of the tissue that forms a sac around the heart. Myocarditis is diagnosed based on history, electrocardiogram (ECG) changes, and cardiac biomarker elevations. The ECG shows any impairments to the heart muscle. Additionally, a magnetic resonance imaging (MRI) image can show any other issues. It's unclear what specific mechanisms trigger immune system reactions to mRNA-based COVID-19 vaccines.

The evidence suggests that this is a rare complication, and occurs after administration of the 2nd dose. It's hard to estimate the true incidence rate.

The best data about myocarditis after mRNA vaccines comes from Israel. The Israeli Ministry of Health posted data about 121 myocarditis cases occurring within 30 days of a 2nd dose of mRNA vaccine out of 5,049,424 persons. This suggests a crude incidence rate of approximately 24 cases per million. Updated information is accessible at: https://www.gov.il/en/departments/news/01062021-03

Advice and Recommendations

Vaccinated people can usually go back to normal activities after their symptoms improve. They should speak with their doctor before going back to exercise or sports. Avoid strenuous exercises within one week of vaccination, keep rested and well-hydrated. Unless symptoms persist, the 2nd dose is important to achieve the maximal immunity benefits.

It’s important to consider vaccine-associated myocarditis within the context of the pandemic. Infection with SARS-CoV-2 is a clear cause of serious cardiac injury in many patients. The mechanism of injury may be infection, an immune-mediated response, or a combination of direct or indirect effects. Given that COVID-19 vaccines are effective at preventing infection, we should weigh any risk against the benefit.