Are Covid vaccines responsible for myocarditis? The conclusions of a new study – L’Express

During the Covid-19 crisis, vaccines were the main weapon to reduce the number of hospitalizations and deaths. In particular, the messenger RNA (mRNA) vaccines developed by Pfizer and Moderna. However, these have been associated with various risks of adverse effects, like all treatments. One of them has attracted the attention of researchers, because it is rarely observed with other drugs or vaccines: myocarditis. This is an inflammation of the heart muscle, most often caused after a viral infection, which causes mild symptoms most of the time, but can require a few days of observation in hospital, or even cause cardiac complications.

Studies had already shown that there was a low risk of myocarditis within seven days of mRNA vaccination and within thirty days of Covid-19 infection. However, the long-term prognosis of patients with post-vaccination myocarditis was until now unknown. A team of researchers led by Mahmoud Zureik, professor of epidemiology and public health and director of Epi-Phare (1), has just published a new study, consulted by L’Express and published this Monday 26 in the Journal of the American Medical Association (JAMA)They followed the patients concerned eighteen months after their vaccination or infection: “Faced with an undesirable side effect almost never observed with a vaccine before, we wanted to know what happened, in the long term, to these people”, explains Prof. Zureik.

0.186% risk of myocarditis after vaccination

To carry out this work, the researchers first identified all people aged 12 to 49 hospitalized in France for myocarditis between December 27, 2020 and June 30, 2022. They then separated these patients into several groups: those with post-vaccination myocarditis, i.e. whose complication was recorded seven days or less after their vaccination; those affected by post-Covid myocarditis, between eight and thirty days after contracting Covid-19; and those with myocarditis unrelated to either Covid or the vaccines. All vaccinated people were vaccinated with the first-generation injections, since those adapted to Omicron arrived after the period studied.

“Thanks to our first study on post-vaccination myocarditis published in July 2022we know that when a vaccination causes myocarditis, the phenomenon necessarily occurs between one and seven days at the latest, with a median of four days, otherwise, it is not due to the injection,” says Professor Zureik. Similarly, his team confirmed that myocarditis can be attributed to Covid-19 if it occurs up to thirty days after an infection. Beyond that, there is no link and it is conventional myocarditis. This first study had also shown that the percentage of myocarditis occurring after a vaccination was 0.002%, or one in every 50,000 vaccinations. The maximum frequency occurred in young men, after the second injection of the Moderna vaccine (0.016%, or one in 6,012 people), the lowest in women after a first dose of Pfizer (one in 200 to 300,000 people).

In their new study, the researchers indicate that in total, in France, 4,635 individuals were hospitalized for myocarditis during the period studied, including 558 for myocarditis after a vaccine, 298 for myocarditis after a post-Covid infection and 3,779 for conventional myocarditis. “We also know that 30 million people aged 12 to 49 were vaccinated with ANRm during this same period,” adds Professor Zureik. The frequency of post-vaccination myocarditis found in this study is 0.0186%, which confirms the results of previous research.

Young men more often affected by post-vaccination myocarditis

The researchers then followed all of these patients for eighteen months after their admission to the hospital in order to measure the occurrence of complications occurring after their myocarditis, for example a readmission to the hospital, a hospitalization for another cardiovascular event, a death, etc. “We also studied the medical care of patients upon discharge from hospital (medical examinations, treatments, etc.),” ​​explains Professor Zureik.

They confirmed that patients with post-vaccination myocarditis were younger than those with post-Covid or conventional myocarditis and were more likely to be male, and found that a very small proportion of them required medical care several months after discharge. The researchers also determined that eighteen months after hospitalization, patients with myocarditis attributable to mRNA Covid-19 vaccination had fewer complications (5.7%) than patients with Covid-19 myocarditis (12.1%) and patients with conventional myocarditis (13.2%).

Thus, as shown by the results presented in their study, patients with post-vaccinal myocarditis were less often subject to re-hospitalization for myocarditis (3.2%, compared with 4% for post-vaccinal myocarditis and 5.8% for conventional myocarditis), but also less often subject to other cardiovascular complications (2.7%, compared with 7.4% and 7.3%), heart failure (1.1%, compared with 3.7% and 3.5%), or hospitalizations for other causes (12.2%, compared with 21.1% and 19.6%). They also had a lower death rate (0.2%, compared with 12.1% and 13.2%), although these deaths recorded were for any cause, and therefore not necessarily related to myocarditis.

This study therefore adds to the long list of scientific works that confirm that the benefit-risk balance is in favor of vaccination. “Our work also helps to fill a gap in the knowledge racket, while billions of people have been vaccinated on the planet, and the effectiveness of vaccines and their side effects are still being studied,” assures the director of Epi-Phare.

The most ardent critics of vaccination might retort that people who were neither vaccinated nor infected would probably not have had myocarditis. “Of course, at the individual level, we can hear the criticism, but there were 558 cases of post-vaccination myocarditis in France for 30 million vaccinated people and, even if we can estimate that Covid-19 was less serious in this age group, there were still 100,000 hospitalizations and 1,100 deaths among 12-49 year-olds, 90% of whom were not vaccinated,” replies Professor Zureik. A study published in the journal Epidemics in February 2024 by researchers from the Bordeaux University Hospital, the National Institute of Health and Medical Research (Inserm) and the National Institute for Research in Digital Science and Technology (Inria) also confirms that without the vaccination campaign, the number of victims of the Covid-19 pandemic would have been twice as high in France.

(1) Epi-Phare is a public scientific interest group (ANSM-CNAM), to which we also owe one of the largest major studies on the effectiveness of anti-Covid vaccines (22 million people included), in-depth work on the risk factors of Covid-19, but also groundbreaking analyses of all the public health scandals of recent years: Mediator, DepakineEssure, Androcur…