Covid-19 vaccines have saved many lives during the pandemic. But they are still drugs, and therefore are not free from side effects, potentially even serious ones. It has always been said that in this case the safety profile, especially for mRNA vaccines, was favorable – that the dangers of the vaccines were lower than those of the disease – and a new French study confirms the predictions: myocarditis linked to mRNA vaccines would in fact be much milder than that caused by the disease, as well as that which develops for other causes in the population.
The research, published in the journal Jama Network, was conducted using the French health system database. The authors collected all reports of hospitalizations for myocarditis that occurred in people aged between 12 and 49 years from December 2020 to June 30, 2022. They then divided the hospitalizations into vaccine-induced myocarditis (hospitalized within 7 days of vaccination), post-Covid myocarditis (occurring within 30 days of hospitalization for Covid) and myocarditis of other nature (not included in the two previous groups), and evaluated how the course changed between the three groups of patients.
In total, hospitalizations for myocarditis recorded in the period under examination were 4,635, of which 558 for vaccine-induced myocarditis (the majority, 376, after the second dose), 298 for post-Covid myocarditis, and the remaining 3,779 for other causes. Patients with vaccine-induced myocarditis were on average younger (average age 25 years, compared to 31 for post-Covid patients and 28 for those for other causes), and mostly male (84%, compared to 67% for Covid-induced myocarditis and 79% for those for other causes).
Among patients with post-vaccination myocarditis, 18 were re-hospitalized for myocarditis after being discharged, 15 suffered other cardiovascular events or complications, and one death was recorded. For patients with post-covid myocarditis, there were 12 hospital readmissions, 22 other cardiovascular events, and 4 deaths. Finally, for myocarditis not related to vaccines and Covid, there were 277 hospital readmissions, 49 other cardiovascular events, and 17 deaths. By evaluating the different incidence rates of myocarditis in the three groups, and confounding factors such as age, sex, region of origin, lifestyles, and comorbidities, the researchers calculated that the risk of a second hospitalization, other cardiovascular events, and death is lower in the case of post-vaccination myocarditis, compared to both those caused by Covid 19 and those with other causes.
How to interpret the data? These are certainly reassuring results, which confirm that myocarditis is a very rare side effect in the case of mRNA vaccines against Covid, and that it tends to be mild, and to have a more benign hospital course than that caused by the virus or other causes. In light of this, the researchers point out that patients who develop myocarditis after anti-Covid vaccination are mostly young and otherwise healthy people, and that myocarditis may require medical attention even for months after discharge from the hospital. A danger that should therefore not be underestimated in the future, especially given the absolutely benign course that Covid 19 tends to have in patients under 30.