Moderna’s COVID-19 vaccine is up to four times more likely to cause inflammation of the heart muscle than its rival vaccine from Pfizer, according to a Danish study published in the British Medical Journal on Thursday (Dec. 16).
The study, in which almost 85% of Danes aged 12 and older participated, investigated the link between mRNA-based COVID-19 vaccines and heart inflammation—known as myocarditis or myopericarditis—after earlier studies from Israel and the U.S. indicated an increased risk of heart inflammation after inoculation with the Pfizer and Moderna injections.
“Vaccination with mRNA-1273 (Moderna’s vaccine) was associated with a significantly increased risk of myocarditis or myopericarditis in the Danish population,” the study said.
“In general, the rate of myocarditis or myopericarditis was about threefold to fourfold higher for mRNA-1273 (Moderna) vaccination than that for BNT162b2 (Pfizer-BioNTech) vaccination.”
The researchers found 1 case per 71,400 vaccinated with Pfizer and 1 case per 23,800 vaccinated with Moderna. Most of the cases are mild, according to the study.
Pfizer’s COVID-19 vaccine was only associated with a higher risk of heart inflammation among women in the study, contrasting with the results of the studies from Israel and the US.