Academic journal

Heart problems after Covid-19 bites very rare but research lacks clarity

PARIS — Research shows that the risk of developing heart disease after a messenger RNA vaccine against Covid-19 is very low, and should not call into question the value of life-saving vaccination campaigns deployed around the world.

But the risk is “not negligible”, and the available evidence is difficult to assess accurately, researchers said, calling for better data on the subject.

“The fact that we are now over a year and a half into mass mRNA vaccination and still do not have certainty about the incidence of this clinically important outcome is disappointing,” the US researchers wrote. Dr Jing Luo and Dr Walid Gellad in a commentary in the BMJ Journal in mid-July.

Their opinion piece was based on a large study in the same issue that reviewed available research on the frequency of myocarditis and pericarditis, two inflammations of the heart, after vaccination with Pfizer mRNA injections. and Moderna.

This is a delicate subject for the scientific community. The risks were quickly identified after the launch of mass vaccination campaigns last year, but were then greatly exaggerated by vaccine skeptics seeking to oppose at all costs.

Heart problems were very rare after vaccination and mostly did not cause serious complications. The fact that Covid-19 itself poses cardiovascular risks is also part of the equation.


Thus, the value of mRNA vaccines has not been questioned. But for the BMJ researchers, the current state of knowledge on the risks remains insufficient.

“Clearly, the incidence of myocarditis is rare after vaccination,” they wrote. “Scarcity remains a matter of major importance.”

The review they commented on, in which other researchers analyzed the results of around 50 previous studies, provides answers.

This largely confirmed previous findings, including that the risk of myocarditis after vaccination appears to be higher in young men than in any other group.

And, although the conclusions are less clear, there also appears to be a slightly higher risk after a dose of Moderna’s vaccine, compared to Pfizer’s.

This would seem to reinforce the decision of some countries, including France, to only allow people over the age of 30 to receive the Moderna vaccine. Other countries like the United States have made no such distinction.

The research highlighted a lack of clarity in other areas.

He found that some results could vary widely based on different methodologies while others could be considered unsatisfactory.

This was the case for a particularly sensitive subject: the vaccination of children.

Many countries have allowed vaccination of young children, but adoption has often been slow in part due to parental reluctance.

Myocarditis in children aged five to 11 is “very rare”, the researchers said, but added that “the certainty is low”.


The researchers raised other questions.

Most cases of myocarditis and pericarditis resolved without serious illness. But they were rarely followed for a long time, meaning they couldn’t rule out future complications.

The research was also unclear as to whether a booster dose posed as much risk as the initial vaccination.

This could be a pressing question as many developed countries with widely immunized populations wonder how often they should deploy additional doses.

However, a French study published on Friday shed some light on the subject.

The study, which has not yet been peer-reviewed or published in a scientific journal, was conducted by Epi-Phare, which is part of the French drug safety agency ANSM, looking at health data public of millions of French people.

He found less risk of myocarditis from booster doses of the Pfizer and Moderna vaccines than from the initial vaccination.

“Furthermore, the risk decreases with the duration between each successive dose,” the researchers said. AFP