(Bloomberg) — The risk of rare heart inflammation side effects was as much as four times higher in people who received Moderna Inc.’s Covid-19 shot than in those who got the vaccine from Pfizer Inc. and BioNTech SE, according to researchers in Denmark.
About 4.2 people per 100,000 who got the Moderna vaccine developed myocarditis or myopericarditis within 28 days of vaccination, with the highest risk seen in those age 12 to 39 and after people received their second doses, according to the study, which was published in the BMJ.
With the Pfizer shot, meanwhile, 1.4 people per 100,000 developed the rare heart side effects, although a heightened risk was observed in women, the study said.
The prevalence of such side effects was nonetheless low and when it occurred, people had “predominantly mild” experiences, the authors wrote. The greater health risks by far were seen in the unvaccinated, who, among other things, had a 14-fold increased risk of cardiac arrest and death in the 28 days following a positive test, the researchers said.
The research “supports the overall benefits of such vaccination on an individual, societal, and global level,” wrote the authors, led by Anders Husby, a researcher of epidemiology and biostatistics at Imperial College London.
Moderna’s messenger-RNA shot contains more genetic material than Pfizer’s, which may help explain the increased side effect profile, the company has acknowledged. Each dose contains 100 micrograms of mRNA encased in lipid nanoparticles, compared to just 30 micrograms per dose in the Pfizer-BioNtech vaccine.
The study draws on a year’s worth of Danish healthcare data covering 4.9 million people, the majority of the country’s population.
Earlier this week a study from the University of Oxford found that the rare form of heart inflammation some people get after a Covid shot occurs far less often in response to vaccination than after the disease itself. The scientists found that the number of cases of myocarditis was at least four times greater after Covid-19, according to the largest study to date on the topic.
Moderna did not respond immediately to a request for comment.
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