A meta-analysis of four cohort studies from four Nordic countries (23,1 million residents) was recently published and presented relevant data on Covid-19 vaccination. In the 16-24 age group, those vaccinated with two doses of different mRNA vaccines (Pfizer and Moderna) or men vaccinated with two doses of the same vaccine have a higher incidence (within 28 days) of myocarditis than those infected (test positive).
This study, published in Jama Cardiology, concludes that the frequency of myocarditis after vaccination with different vaccines is 20 times higher in young men aged 16-24 years and 10 times higher in young women of the same age group.
Incidence of myocarditis in young people after a positive test
*Although this may not be accurate, for simplicity of language we will generically call those who have tested positive (suspected infection) ‘infected’.
As the tables below show, myocarditis after infection is residual from age 12 to 15 years and has an incidence of 0,37 in girls and 1,37 in boys aged 16 to 24 years per 100.000 positive test persons.
Myocarditis after two doses of different vaccines
Compared with the incidence after infection, we conclude that the frequency of myocarditis after double vaccination with different mRNA vaccines is about 20 times higher in the “16-24” male age group.
In girls of that age, the frequency is 10 times higher.
Myocarditis after two doses of similar vaccines
When the vaccines are from the same company, for boys the incidence was four times higher with the Pfizer vaccines and 13,5 times higher for the Moderna vaccines, in relation to the incidence after testing positive for SARS-CoV-2.
In young girls the incidence is similar when vaccination was done with Pfizer only. We have no data on double vaccination with Moderna in this female age group.
Supplementary content – eTable 5.
The incidence of myocarditis in this age group after only one dose of vaccine is similar (within the margin of error) to the incidence after infection (positive test). For females, again there are no data for the Moderna vaccine.
Both incidences, of vaccination and infection, are calculated after 28 days.
Limitations
The study has as its strength a very large sample and is based on official data. However, there are limitations. For this study, all hospital admissions resulting from a diagnosis of myocarditis are considered as one event of myocarditis or pericarditis.
This article was written in co-authorship with Rui Lima.
