Pfizer and Moderna vaccines: the risk of myocarditis and pericarditis confirmed, but uncommon

An increased risk, but a rare frequency. A large French study carried out on nearly 2,000 patients hospitalized in the country during the summer, published on Monday, confirms the direct link between vaccination against Covid-19 and the risk of developing myocarditis or pericarditis. But this risk remains infrequent and does not call into question the benefit of the injection, according to scientists.

Led by the Epi-Phare structure, which brings together Health Insurance and the National Medicines Agency, this case-control study focused on people aged 12 to 50 years hospitalized in France for myocarditis or pericarditis between the 15th May and August 31, 919 cases of myocarditis and 917 cases of pericarditis. These two disorders are inflammations of the heart. The first affects the myocardium, the main heart muscle, and the second the pericardium, the membrane that surrounds the heart.

As had been shown by pharmacovigilance reports, the results of the French study confirm that Pfizer and especially Moderna vaccines increase the risk of these diseases occurring within seven days after vaccination. Each case was compared to ten “controls”, who have the same age, sex and department of residence, but did not have myocarditis. The risks of hospitalization for myocarditis or pericarditis were thus compared between vaccinated and non-vaccinated in otherwise similar situations.

These risks appear to be more marked, even if low, in men under 30, especially after the second dose of Moderna. Vaccination with the latter would thus be the cause of 132 additional cases of myocarditis per million doses administered. In women under 30, the excess myocarditis attributable to the second dose of Moderna is estimated to be in the order of 37 per million doses.

As for the risk of pericarditis, it also appears more marked after the Moderna vaccine in those under 30 years of age, in particular after the second dose which would be the cause of an excess of cases of about 18 per million doses in young men. Note, however, that no death has been reported among people hospitalized for these conditions when they follow vaccination.

As a precaution, the Moderna vaccine was suspended in mid-October for booster doses. The government is now waiting for an opinion from the High Health Authority to authorize it again, or not.

“When we weigh the effectiveness of vaccines against severe forms of Covid-19 (estimated at around 90%) and these existing risks, but infrequent, and with the favorable evolution, the benefit-risk ratio of vaccines is not called into question “, tempers with AFP Mahmoud Zureik, director of the Epi-Phare structure.

At the end of August, an American study had already confirmed the increased risk of developing myocarditis after vaccination with messenger RNA. But this work had shown that the possibility of suffering from such disorders remained much higher during a Covid-19 infection. According to American researchers, patients infected with the virus are, on average, almost sixteen times more likely to develop myocarditis than the rest of the population.