As part of the reinforced surveillance system for vaccines against Covid-19, the EPI-PHARE group has conducted a new pharmacoepidemiology study on the risk of myocarditis after injection of an mRNA vaccine from Pfizer laboratories (Comirnaty ) and from Moderna (Spikevax).
According to new data relayed by the ANSM on July 22, 2022, the risk of myocarditis is increased but remains low after the first booster dose of an mRNA vaccine and this risk decreases with the lengthening of the time between doses. This is what emerges from the new study carried out in particular by the National Medicines Safety Agency (ANSM).
The risk of myocarditis would be increased for the first booster dose (third dose), although less markedly than after the second dose, and would decrease with the lengthening of the duration between doses.
In the majority of cases, the patient’s condition improves on its own or with the help of treatment. The risk of myocarditis after an injection remains globally “very rare”: that is to say less than 1 per 10,000 vaccinated. Young men are most at risk. In all cases, “These pharmacoepidemiological data do not call into question the benefit/risk ratio of the vaccines against Covid-19 Comirnaty and Moderna, whose efficacy against severe forms of Covid-19 is around 90%”still indicates the ANSM.
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A previous study conducted by EPI-PHARE, the results of which were published in the journal Nature Communications, had shown that there was a risk of myocarditis in the week following vaccination against Covid-19 by mRNA vaccines, in particular after the second dose of the Spikevax vaccine in men and women aged 12 to 50 years. This previous study had also confirmed the favorable clinical evolution of cases of myocarditis.
EPI-PHARE is a scientific interest group in the epidemiology of health products created by the national drug safety agency (ANSM) and the French health insurance.
In a latest study published on July 22, there is indeed the existence of a risk of myocarditis after the first booster dose (third dose). This risk is lower than after the second dose and decreases with increasing time between successive doses.
Based on data from the National Health Data System (SNDS), EPI-PHARE has carried out a new study aimed at measuring the effect of the first booster (third dose) and the delay between doses of the other on the risk of myocarditis. The study included the 4,890 cases of myocarditis in people aged 12 or over, admitted to French hospitals between December 27, 2020 and January 31, 2022, as well as 48,900 controls.
The risk of myocarditis is increased during the first week following administration of the third dose of Comirnaty and Spikevax vaccines, but with a lower risk for the third dose compared to the second.
In more detail, the excess of cases of myocarditis associated with the third dose is globally estimated at 0.25 cases per 100,000 doses of the Comirnaty vaccine and 0.29 cases per 100,000 doses of the Spikevax vaccine, corresponding to 1 case of myocarditis attributable to vaccination for the administration of 398,000 third doses of Comirnaty and 340,000 third doses of Spikevax.
The largest excess cases were observed in men under 30 years of age, with a maximum of 1.2 cases per 100,000 third doses of Comirnaty, which corresponds to 1 case of myocarditis per 87,000 third doses.
This study thus shows on the one hand that the risk of myocarditis is increased for the first booster dose (third dose), although less markedly than after the second dose, and on the other hand that it decreases with lengthening of time between doses. However, myocarditis associated with mRNA vaccines remain infrequent events with regard to the number of people exposed.
Myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the membrane that surrounds the heart) are usually caused by a viral infection such as Covid-19 and tend to occur in young men. In the majority of cases, the patient’s condition improves on its own or with the help of treatment.