MEDICAL ADVISORY: mRNA COVID-19 Vaccines and Myocarditis Issued by: M. Mustafa Hirji, MD, MPH, FRCPC, Medical Officer of Health & Commissioner (Acting) On June 30, 2021, Health Canada updated the product monographs for the mRNA COVID-19 vaccines (Pfizer-BioNTech,
Moderna) to include very rare reports of myocarditis and pericarditis following vaccination. On July 2, 2021, in light of these changes, the National Advisory Committee on Immunization (NACI) provided updated advice on second doses for individuals who experienced myocarditis and/or pericarditis after receiving a first dose of an mRNA vaccine. NACI Recommendations - NACI recommends that people who are offered an mRNA COVID-19 vaccine should be informed of the very rare risk of myocarditis and/or pericarditis following immunization and should be advised to seek immediate medical
attention if they develop symptoms, which may include
- Chest pain
- Shortness of breath, or
- The feeling of a fast, pounding or fluttering heartbeat.
- As a precaution, NACI recommends that individuals who experienced myocarditis and/or pericarditis after a first dose of an mRNA vaccine should wait to get their second dose until more information is available
- NACI continues to strongly recommend that a complete series with an mRNA vaccine be offered to all eligible
individuals 12 years of age and older who do not have contraindications
Evidence & Rationale - mRNA COVID-19 vaccines provide very good protection against SARS-CoV-2 infection and symptomatic COVID-19 disease, including severe illness, hospitalization and death
- A small number of cases of myocarditis and/or pericarditis following immunization with mRNA COVID-19 vaccines have been reported in Canada and internationally. As of yet, a causal link has not been established, and these being co-incident but unrelated remains a possibility.
- Based on cases reported internationally, available information indicates that instances of myocarditis and pericarditis after vaccination with an mRNA COVID-19 vaccine occur
- More often after the second dose
- Usually within a week after vaccination
- More often in adolescents and young adults under 30 years of age
- More often in males than females.
- The cases to date have generally been mild, and individuals tend to recover quickly
- Data in Canada are emerging and surveillance is ongoing
- There are many potential causes of myocarditis and pericarditis, including viral infections. It can also occur as a complication in people who are infected with the COVID-19 virus.
- Investigations into an association between myocarditis and/or pericarditis and the mRNA COVID-19 vaccines continue to evolve. NACI will continue to monitor the evidence and will update recommendations as needed.
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