This is a summary, written by members of the CITF Secretariat, of:

Naveed Z, Li J, Wilton J, Spencer M, Naus M, Velásquez García HA, Kwong JC, Rose C, Otterstatter M, Janjua NZ; Canadian Immunization Research Network (CIRN) Provincial Collaborative Network (PCN) Investigators. Comparative Risk of Myocarditis/Pericarditis Following Second Doses of BNT162b2 and mRNA-1273 Coronavirus Vaccines. J Am Coll Cardiol. 2022 Nov 15;80(20):1900–8, DOI:

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

A paper by Drs. Naveed Janjua and Zaeema Naveed (British Columbia Centre for Disease Control), and CITF-funded researchers from the Canadian Immunization Research Network (CIRN), including Dr. Jeff Kwong (University of Toronto), published a paper in the Journal of the American College of Cardiology that evaluated the odds of developing myocarditis or pericarditis as a result of receiving two doses of either the Pfizer or Moderna mRNA vaccines against COVID-19. From a sample of more than 3 million people, a total of 59 cases of myocarditis and 41 pericarditis events were observed, affirming the rarity of this particular side effect.

Key points:

  • The study directly compared participants who received two doses of mRNA vaccines (Pfizer n=2.2 million people, Moderna n=0.9 million people).
  • Overall rates of myopericarditis were still very low for both vaccine products, however, a total of 59 cases of myocarditis and 41 pericarditis events were observed.
  • Researchers observed two- to three-fold higher odds of myocarditis among individuals who received Moderna compared to Pfizer. These increased odds were only seen in younger (18-39 years old) compared to older (over 40 years old) individuals.
  • The association between mRNA products and myocarditis was stronger for men compared to women.
  • Most vaccine-related myocarditis and pericarditis events tended to be mild and resolved without intervention.

Unlike previous studies, researchers here directly compared both mRNA vaccine products used extensively in Canada to demonstrate the incidence of rare, but potentially critical side effects. These results may potentially help define vaccine policy on choices of vaccines offered for different age groups.

Overall, 52 million doses of Pfizer and 22 million doses of Moderna have been administered in Canada. As of March 2022, a total of 1933 cases of myocarditis/pericarditis have been reported in Canada. Few population-based analyses have been conducted to directly compare the incidence of such safety events among the two mRNA vaccines.