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Researchers retract preprint study that miscalculated higher heart inflammation risk for Moderna, Pfizer COVID vaccines

In the past few weeks, anti-vaxxers have rallied behind a nonpeer-reviewed study by a group of Canadian researchers as evidence against COVID-19 vaccines. Turns out, the paper made a fatal mistake in reaching its conclusion.

Scientists at The University of Ottawa Heart Institute have retracted the preprint study, which falsely calculated a 1 in 1,000 risk of heart inflammation for Moderna’s and Pfizer-BioNTech’s mRNA COVID vaccines.

The study authors have withdrawn the manuscript “because of a major error pertaining to the quoted incidence data,” the team said in a retraction statement on Sept. 24.

For the research, the team collected two months of data from the Public Health Agency of Ottawa on people who had received an mRNA COVID-19 shot and calculated the incidence of myocarditis or pericarditis—inflammation of the heart muscle or the heart’s membrane—within one month after vaccination.

In the original paper, published on the preprint site medRxiv on Sept. 16, they identified 32 patients with the heart problem and 32,379 doses administered in total, leading to an estimated 1 in 1,000 rate.

However, the actual number of administered doses during the period was over 800,000, the researchers note in their retraction statement. That would put the correct incidence rate at about 1 in 25,000, or 4 in 100,000. A recent peer-reviewed study based on data in Israel has put the risk of myocarditis for Pfizer and BioNTech’s Comirnaty at 2.7 events per 100,000 persons.

In its short life on the medRxiv site, the study with the wrong data was retweeted over 15,000 times, according to Almetric.

Preprints are set up as a way for scientists to share early information on research findings. But critics have been pointing to the lack of the rigorous peer-review process, which could pick out such flaws.

The U.S. FDA in June added a warning about the rare risk of heart inflammation in the fact sheets for Pfizer-BioNTech’s and Moderna’s COVID-19 vaccines. At the time, the combined heart inflammation cases for the two mRNA vaccines were 12.6 per million doses, according to the CDC. The side effect is believed to affect males under the age of 30 more than other populations.

Noting the heart inflammation problem is very rare, the CDC has concluded that the benefits of the vaccine outweigh these risks and continues to recommend that everyone aged 12 years and older get vaccinated.