Myocarditis after mRNA vaccine is rare

Researchers at ProCardio, in close collaboration with cardiology centres across Norway, the Norwegian Institute of Public Health (FHI) and the Norwegian Medicines Agency (DMP), have conducted the first national validation study of myocarditis following COVID-19 vaccination in Norway. The study includes 4.1 million vaccinated individuals and identified 177 cases where the vaccine was considered the most likely cause of myocarditis—corresponding to 4.5 cases per 100,000.

Through comprehensive review of clinical records, the researchers found that approximately half of the initially reported cases had alternative explanations. This highlights the strength of the methodological approach, combining clinical expertise with nationwide health registry data to ensure accurate and reliable estimates.

The cases were most common among younger men and after the second vaccine dose. However, the clinical course was generally mild: most patients had short hospital stays, few required intensive care, and nearly all preserved normal cardiac function.

The findings confirm and strengthen existing international evidence and represent an important contribution from Norwegian research environments to the global knowledge base on vaccine safety. The study also underscores the value of the national collaboration led by ProCardio, involving contributions from more than 20 hospitals.

Overall, this work demonstrates Norway’s ability to conduct high-quality, clinically grounded registry research—with direct relevance for safer and more informed vaccine recommendations.