Inflammation of the heart muscle

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Myocarditis cases were most common after Covid-19 vaccination with an mRNA vaccine after the second dose.

(Bild: AP)

Cases of heart muscle inflammation (myocarditis) following mRNA Covid-19 vaccination, especially in young people, have occasionally caused concern in recent years.

However, these illnesses were consistently milder than cases of myocarditis resulting from Covid-19 disease or other causes. This has now been proven by French scientists.

Laura Semenzato and her co-authors from the French Medicines Agency (ANSM) have published their study in the Journal of the American Medical Association (JAMA; DOI: 10.1001/jama.2024.16380). Their aim was to investigate the long-term complications of people with myocarditis (observation period: one and a half years) between the end of December 2020 and the end of June 2022. They had access to the data of all those affected in France.

85 percent of those affected were men
The scientists: "A total of 4635 people were hospitalized for myocarditis. There were 558 after a vaccination, 298 after a Covid-19 disease and 3779 patients due to 'conventional' myocarditis." Myocarditis cases were most common after Covid-19 vaccination with an mRNA vaccine after the second dose. 85 percent of those affected were men.

(Bild: stock.adobe.com)

Risk of corona disease significantly higher
The risk of further complications within 18 months was very unevenly distributed and indicates a significantly lower risk after a Covid-19 vaccination than after a real disease caused by SARS-CoV-2 or other causes of myocarditis. For example, 5.7 percent of people had to be hospitalized again for cardiovascular problems after myocarditis in probable connection with a vaccination. After Covid-19 myocarditis (illness), however, the figure was 12.1 percent within one and a half years, i.e. significantly higher. This risk was even slightly higher - at 13.2 percent - for patients with "conventional" myocarditis. Myocarditis can have a wide variety of causes.

Between the two vaccines, there was a lower risk of myocarditis after vaccination with the Moderna mRNA vaccine (mRNA-1273) compared to the BioNTech/Pfizer vaccine (BNT162b2). However, the difference was not statistically significant. One patient from the mRNA myocarditis group died within 18 months. This meant a mortality rate of 0.2 percent. In contrast, four people from the group with myocarditis after Covid-19 disease (1.3 percent) and 49 patients after "conventional" myocarditis (also 1.3 percent) died.