Moderna’s COVID vaccine is up to four times more likely to cause heart muscle inflammation, a very rare side effect, than its rival from Pfizer-BioNTech, according to a Danish study published in the British Medical Journal.
The study, which involved 4.9 million people over the age of 12, or nearly 85% of Danes, investigated the relationship between mRNA-based COVID-19 vaccines and inflammation of the heart, also known as myocarditis or myopericarditis. .
Previous studies in Israel and the United States indicated an increased risk of heart inflammation after inoculation with the mRNA vaccines developed by Pfizer-BioNTech and Moderna.
“Vaccination with mRNA-1273 (Moderna’s vaccine) was associated with a significantly increased risk of myocarditis or myopericarditis in the Danish population,” the study notes.
However, the overall risk of heart inflammation from vaccines, both based on mRNA technology, was low, according to the study, conducted by researchers at the Statens Serum Institute in Denmark.
“Overall, the rate of myocarditis or myopericarditis was three to four times higher for the mRNA-1273 vaccine (Moderna) than for the BNT162b2 vaccine (Pfizer-BioNTech),” the study notes.
The researchers found only one case for every 71,400 vaccinated with Pfizer-BioNTech and one case for every 23,800 vaccinated with Moderna. Most of the cases were mild, according to the study.
The Pfizer-BioNTech vaccine was only associated with an increased risk of heart inflammation among women, according to the study, which contrasts with the results of the Israel and the United States studies.
The authors said the discrepancy could be explained by the median age of the vaccinated population, the length of time between the first and second injections, or because fewer Danes had tested positive for COVID-19.
“Our findings do not overall overshadow the many benefits that vaccination brings,” study author Anders Hviid said in a statement.
“Keep in mind that the alternative of contracting a COVID-19 infection probably also carries a risk of inflammation in the heart muscle,” Hviid said.
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