But absolute number of heart inflammation cases was low, authors said.
A study published in the British Medical Journal late Thursday suggests Moderna’s COVID-19 vaccine is up to four times more likely to cause heart inflammation—myocarditis or myopericarditis—than Pfizer-BioNTech’s COVID-19 vaccine.
“Vaccination with [Moderna’s vaccine] was associated with a significantly increased risk of myocarditis or myopericarditis in the Danish population,” and the rate was “threefold to fourfold higher” with the Moderna vaccine compared to the Pfizer-BioNTech vaccine, authors said in the study, which spanned almost 85 percent of Danes, or 4.9 million people aged 12 and older.
The increased risk of myocarditis or myopericarditis with the Moderna vaccine was “primarily driven by an increased risk among individuals aged 12-39 years,” said the researchers, from Denmark’s Statens Serum Institute.
The population-based cohort study, published Dec. 16 in the British Medical Journal (the BMJ), also corroborated previous studies and reports such as those from Israel and the United States that say there is an increased risk of myocarditis or myopericarditis with taking the mRNA-based Moderna or Pfizer vaccines.
Absolute Number of Cases ‘Low,’ Most Were ‘Mild’
Authors of the study wrote that the absolute rate of myocarditis or myopericarditis the mRNA-based vaccine “was low, even in younger age groups.
“The benefits of SARS-CoV-2 mRNA vaccination should be taken into account when interpreting these findings,” they added. “Larger multinational studies are needed to further investigate the risks of myocarditis or myopericarditis after vaccination within smaller subgroups.”
In the study, researchers analyzed nationwide registers in Denmark that show the country’s population data on vaccination, hospital admissions, and results of laboratory assays of blood samples.
Within 28 days of vaccination, they found an absolute rate of myocarditis or myopericarditis for the Pfizer vaccine at 1.4 per 100,000 people (or about 1 case per 71,400), and for the Moderna vaccine at 4.2 per 100,000 people (or about 1 case per 23,800), according to the study results.
Most of the cases were “predominantly mild,” the authors wrote.