No cases of myocarditis (inflammation of the heart muscle) or pericarditis (inflammation of the lining around the heart) were observed in the clinical trials of the COVID-19 mRNA vaccines in children 5-11 years of age. However, due to the number of study participants in the clinical trials, adverse events occurring at a frequency of less than 1 in 1,000 may not have been detected.
Cases of myocarditis and pericarditis have been reported following vaccination with COVID-19 mRNA vaccines in Canada and internationally among individuals aged
12 years and older who received the 30 mcg formulation of the Pfizer-BioNTech COVID-19 vaccine or 100 mcg formulation of the Moderna COVID-19 vaccine; however, the risk is considered rare.
Cases of myocarditis/pericarditis following COVID-19 mRNA vaccination occur most commonly in adolescents and young adults (12 to 30 years of age). It usually occurs within a week of vaccination and is more common:
- after the second dose
- in males than females
- after receipt of the Moderna vaccine than the Pfizer-BioNTech vaccine.
The highest rate of myocarditis reported in Canada in association with the Pfizer COVID-19 mRNA vaccine has been for males aged 12 to 17 years following the 2nd dose, with about 7 cases per 100,000 doses. In both Canada and the US, no deaths attributed to the COVID-19 mRNA vaccine-related myocarditis have been identified in adolescents or young adults.
Data from the US suggest the risk of myocarditis/pericarditis following mRNA COVID-19 vaccination may be higher in older adolescents aged 16-17 years compared to younger adolescents aged 12-15 years.5 In addition, surveillance data suggests that the risk of myocarditis/pericarditis within 7 days of receipt of the second dose of the pediatric Pfizer-BioNTech vaccine may be substantially lower in 5-11 year old males compared to adolescents who received the adult/adolescent Pfizer-BioNTech vaccine.6
Symptoms of myocarditis/pericarditis can include shortness of breath, chest pain, or the feeling of a rapid or abnormal heart rhythm. Symptoms can be accompanied by abnormal test results (e.g., electrocardiogram, serum troponins, echocardiogram).7 Available data indicate that most individuals affected have responded well to conservative therapy and have recovered quickly.3
Emerging Canadian safety surveillance data suggest an extended interval between the first and second dose may reduce the risk of myocarditis/pericarditis associated with the second dose of an mRNA COVID-19 vaccine. For children 5-11 years of age the recommended interval between first and second dose is 8 weeks.3
Myocarditis following mRNA COVID-19 vaccination tends to have a similar epidemiologic profile to classic myocarditis (unrelated to COVID-19), as it occurs more commonly in adolescents and young adult males. Classic myocarditis is less common in younger children 5-11 years of age.5
It is unknown whether myocarditis/pericarditis will occur after the lower doses of mRNA present within pediatric COVID-19 vaccines for children 5-11 years of age.3
A Children’s Hospital of Philadelphia article states, “This situation may cause some parents to consider taking a “wait and see” approach, delaying their child’s vaccination until more doses have been administered. However, what many parents don’t realize is that in teens and young adults — the group with the highest occurrence of this side effect — the risk of developing myocarditis is greater following natural infection”. The article included the following estimates for myocarditis following COVID-19 mRNA vaccination compared to myocarditis following COVID-19 infection:
Of 100,000 males aged 16 to 29 years of age, approximately 5 would develop myocarditis after COVID-19 mRNA
vaccination and about 59 would develop myocarditis after COVID-19
If we consider 100,000 females aged 16 to 29, 1 would develop myocarditis after
vaccination and about 39 would develop myocarditis after COVID-19
As such, the risk of experiencing myocarditis is greater in an unvaccinated person than a vaccinated person. Therefore, opting to delay or forgo vaccination to avoid myocarditis is opting to take the risk of developing COVID-19 infection, which could put the child at greater risk of experiencing myocarditis.8