Myocarditis risk significantly higher after Covid infection than Covid vaccine

The American Heart Association study focused on 12 crucial months at the height of the Covid-19 pandemic.

In a detailed analysis of nearly 43 million people, the risk of myocarditis in unvaccinated individuals after Covid infection was at least 11 times higher than in people who developed myocarditis after receiving a Covid vaccine or booster dose, according to new research.

“We found that across this large dataset, the entire Covid-vaccinated population of England during an important 12-month period of the pandemic when the Covid vaccines first became available, the risk of myocarditis following Covid vaccination was quite small compared to the risk of myocarditis after Covid infection,” says first author of the study Martina Patone, a statistician at the Nuffield Department of Primary Health Care Sciences at the University of Oxford in England.

In the study, published in the American Heart Association’s flagship journal Circulation, Patone and colleagues evaluated England’s National Immunisation database of Covid vaccinations for all people aged 13 or older who had received at least one dose of the ChAdOx1 (a two-dose adenovirus-vector Covid vaccine developed by the University of Oxford and AstraZeneca), the Pfizer-BioNTech or the Moderna Covid vaccine between December 1, 2020 and December 15, 2021.

England’s National Immunisation database records were then cross-referenced and matched to the national offices with data on Covid infection, hospital admission and death certificates for the same time period. Individuals were classified based on age and sex to reveal which groups had the highest risk of myocarditis after a COVID vaccine or after COVID infection and hospitalisation.

In the overall dataset of nearly 43 million people, the analyses found:

• 0.007% of people were hospitalised or died with myocarditis during the one-year study period
• People who were infected with Covid before receiving any doses of the Covid vaccines were 11 times more at risk for developing myocarditis during days 1-28 after a Covid positive test
• The risk of Covid infection-related myocarditis risk was cut in half among people infected after vaccination
• The risk of myocarditis increased after a first dose of the ChAdOx1 Covid vaccine, and after a first, second and booster dose of any of the mRNA Covid vaccines. However, the risk of vaccine-associated myocarditis was still lower compared to the risk of Covid infection-associated myocarditis, except for after a second dose of the Moderna vaccine

• Myocarditis risk was found to be higher during days 1-28 after a second dose of the Moderna vaccine for people of all genders and ages, and the risk also persisted after a booster dose of the Moderna vaccine. However, people receiving a booster dose of Moderna were, on average, younger in comparison to those who received a booster dose of the ChAdOx1 or Pfizer-BioNTech vaccine, therefore results may not be generalisable to all adults

“It is important for the public to understand that myocarditis is rare, and the risk of developing myocarditis after a Covid vaccine is also rare. This risk should be balanced against the benefits of the Covid vaccines in preventing severe Covid infection,” said Professor Nicholas Mills of the University of Edinburgh and a co-author of the paper.

Earlier this week research was published showing that mRNA vaccines are safe to be administered to people with heart failure. 

Image credit: Ed Us