Pfizer vaccine and myocarditis: what are the side effects?

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Health authorities monitor the side effects of the four available vaccines. To date, more than 16,000 side effects have been reported.

Administration of a vaccine can be associated with side effects. "As after any vaccination, you may not feel anything or observe side effects, called undesirable. These effects are unpleasant but they are not serious and disappear spontaneously after a few days," indicates the ANSM.

What are the side effects of the Pfizer vaccine?

In a sheet intended for healthcare professionals published in March 2021, the ANSM listed the side effects identified in clinical trials according to their frequency:

Very common side effects (> 1 in 10):

injection site reaction (pain, swelling at the injection site)




shaking chills



Common side effects (> 1 in 100)

injection site reaction (redness)


Uncommon side effects (> 1 in 1,000)

pain in a limb




itching at the injection site

Rare side effects (> 1 in 10,000)

Bells palsy. "Four cases of facial paralysis (Bells palsy) were reported out of the 22,000 vaccinated people in clinical trials in the days after vaccination (3 to 48 days). In most cases, the paralysis resolved in one week later spontaneously or under treatment ".

Pfizer vaccine: is there a risk of myocarditis?

On April 25, Israels Ministry of Health revealed that it was reviewing 62 cases of myocarditis that occurred after the Pfizer vaccine was administered. At this time, no link has been established between this anti-Covid serum and this condition, but research is ongoing.

"Establishing a link would be difficult because myocarditis, a condition that often goes away without complications, can be caused by a variety of viruses and a similar number of cases have been reported in previous years," explained Dr. Nachman Ash, coordinator of response to a pandemic in Israel.

Myocarditis is an inflammation of the heart muscle called myocardium. Most of the time it is benign, usually caused by an infection. Among the symptoms that can alert, we find fever, fatigue, chest pain or palpitations.

Observations in Israel show that this condition is more common in men under the age of 30 who have received Pfizer serum and in people who have received both doses of this vaccine.

In its latest report published on April 30, Ansm said that "the notification of myocarditis in young men in Israel after a second dose of the Comirnaty vaccine led the rapporteurs and the committee to re-analyze the data on myocarditis cases and myopericarditis ". In France, the health authorities registered five cases of myocarditis after the administration of the Pfizer / BioNTech serum. According to the organization, these side effects "do not question the benefit / risk ratio of the vaccine", but "will be subject to specific monitoring and will be shared at European level."

For its part, Pfizer told Reuters that "side effects are regularly and comprehensively reviewed and we have not seen a higher rate of myocarditis than would be expected in the general population. A causal link with the vaccine has not been established." .

Is the Pfizer / BioNTech vaccine associated with risk of death?

On April 9, the ANSM published its twelfth pharmacovigilance report on the adverse effects reported with the Pfizer / BioNTech vaccine. This document included reports of 386 deaths of people who received the Pfizer / BioNTech vaccine. Most of the deceased patients were elderly with comorbidities. But are these deaths related to the administration of the serum?

These reports can be made by the patients doctor or family when their death could potentially be associated with the injection of the vaccine. But according to ANSM, this is rarely the case. "For the Pfizer vaccine, of all the cases of death that have been reported, there is really only one case for which we have asked ourselves about a possible link with vaccination," explained Antoine Pariente, head of the pharmaceutical center.

According to the specialist, this case involved a very old person who had developed reactogenicity syndromes characterized by flu symptoms and fever. "We wondered if they had not contributed to death, in a very fragile person. That is, a particular context that could have favored death. But for Pfizer, it is actually the only case," said Antoine Pariente. "At this point, there is really no evidence to suggest an association between the Pfizer vaccine and the deaths that have been reported so far. "

For the ANSM, "the existing information does not lead to identify a security signal for these events to date", but "they will continue to be the object of a specific follow-up in subsequent reports."

A case of cerebral thrombosis is also one of the remarkable facts pointed out by the ANSM. However, "it presents a clinical picture different from that observed with the Vaxzevria vaccine from AstraZeneca and does not present, like all the thromboembolic events reported with the Pfizer / BioNTech vaccine, of particular specificity in favor of a role for the vaccine.

These side effects do not question the reliability of the Pfizer / BioNTech vaccine. All anti-Covid vaccines are also "safe, effective and will protect you against a disease that can be really dangerous," Steve Pascolo, a research immunologist at the University Hospital of Zurich (Switzerland) recalled in Europe 1 on April 14.

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