What do we know about myocarditis cases reported after vaccines

These are still rare and mild events, but some countries have adjusted their vaccination policies aimed at younger people. Here is what emerges from some studies

(Photo: CDC on Unsplash) Chest pain, the sensation of the heart racing, shortness of breath. Just as it had been with the rare clotting problems reported after the AstraZeneca vaccine, the institutions also reported the symptoms to be particularly careful for myocarditis and pericarditis associated with mRna vaccines. Especially in some segments of the population: that of young men, because here, more than in other sub-populations, the problem seems to arise, albeit rarely. And also have repercussions: not so much on the health condition of those who undergo the vaccine to date, as in vaccination policies. But let's go in order.

Myocarditis and pericarditis

Pericarditis and myocarditis are inflammations of the heart. In particular, in the first case we refer to an inflammation of the pericardium, the lining that protects the heart. In the second, an inflammation affecting the heart muscle itself. They are typically caused by infections, bacterial or viral, or by damage to the heart, the American National Institutes of Health recall, and can lead to arrhythmias or heart failure.

The names of these two conditions have begun to be more popular (and Google Trends confirms this) in recent months, after the arrival, or rather the approval, of mRna vaccines also for adolescents. Because, the Italian Medicines Agency (Aifa) wrote in July - and before the extension of the Moderna vaccine in the adolescent range - "very rare cases of myocarditis and pericarditis have been observed" after vaccinations with mRna. Especially in the days close to the second dose and especially in young men. The same information is found on the Centers for Disease Control and Prevention website, with due caution: in most cases these are non-serious conditions, which are resolved quickly and without aftermath. But certainly, as with any potential side effect associated with vaccines (and any drug), the possible correlation had to and must be investigated.

Reports in Italy

It is not surprising, therefore, that new ones arrive data on the subject alongside the reports recorded by the authorities that are concerned with vaccination surveillance. For example, in recent days, Aifa has released the ninth report on the surveillance of Covid-19 vaccines, which also talks about myocarditis and pericarditis.

In particular, we read, there are 6 cases of myocarditis / pericarditis per million doses administered reported in connection with the administration of Pfizer-BioNTech vaccine, 11 per million doses administered for Moderna. Rare in the younger group - but not specified in number - cases of myocarditis, pericarditis or myopericarditis / perimyocarditis, but always "after administration of mRna vaccines, mainly after the second dose and in male subjects". A correlation discussed not only by pharmacovigilance reports, but also by studies on the subject.

New data on vaccine-related myocarditis

This is the case of the publications that arrived in recent days on the pages of New England Journal of Medicine. One of the two studies analyzed the incidence of myocarditis in two and a half million people in Israel who received at least one dose of Pfizer vaccine, estimating, in the following 42 days, an incidence of about two cases per hundred thousand people, who arrived about 11 cases out of 100 thousand in the case of young males aged between 16 and 29.

The cases, reported more often in the days following the second dose, were mostly mild or moderate, write the authors. But hardly comparable with other studies, due to methodological limitations. That said, they would be higher than some estimates of the US CDCs cited by the authors, who speak of 1.2 cases per 100 thousand children between 18 and 29 years old. But even higher than the incidence in the general population (therefore also including children), considering that we are talking about about 10 cases out of 100 thousand people. This same figure is not certain: it oscillates between 10-22 cases per 100 thousand people, citing an in-depth study on the subject of the Bambin Gesù pediatric hospital in Rome, but according to other sources the incidence would be higher and more common among young men. in general. Estimates last month showed a risk of myocarditis tripled by vaccination, with an excess of 3 events per 100 thousand people.

Another study, also on the Nejm, confirms that the incidence of myocarditis increases after vaccination and results higher in young men, especially after the second dose (analysis referring to cases of myocarditis starting from the data of over 5 million vaccinated). For example, in the 16-19 age group, 34 cases were observed after the second vaccination compared to almost 3 expected, referring to the pre-pandemic two-year period, and 32 compared to 4 in the 20-24 year range. But, on the whole, the paper states, the incidence of myocarditis remains low and "generally mild", even if it is confirmed by an increased incidence in vaccinated compared to unvaccinated.

The decisions of the countries

Despite this, and even if rare, myocarditis remains a problem to investigate in relation to vaccines, the authors conclude, because in some cases they could be serious. For this reason, by applying a sort of principle of caution (also by virtue of the incidence estimates that are still difficult to make), some countries have revised their vaccination policies in young people precisely starting from the data that are accumulating on the subject. Similarly to what had happened after the reports of thrombosis associated with the AstraZeneca vaccine, when fear had prompted some to suspend the anti-Covid Vaxzevria vaccine.

Alongside the aforementioned principle of caution, consideration also finds risk (less, but not entirely absent) of serious cases of Covid-19 and complications in younger people. This, although myocarditis itself is much more common after infection than with vaccination, as scientists recall. That said, some countries seem to have moved: for example, Sweden and Denmark have blocked the use of Moderna's vaccine in adolescents while other countries (such as Norway and Great Britain), summarizes the New York Times, would have chosen the path of only one. vaccination for the youngest.


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