Pericarditis and myocarditis following mRNA vaccination: our review

17 September 2021

The UK’s independent Drug Safety Research Unit (DSRU) has concluded that heart inflammation after mRNA COVID-19 vaccines is very rare and mild in the vast majority of patients, after a review of available data.

But DSRU is calling for pharmacoepidemiological research to better understand the heart events, as more younger people are due to start receiving mRNA vaccines.

DSRU compared data from the UK, the US and Europe about the reporting rates of myocarditis and pericarditis – an inflammation of the heart muscle and protective sack that surrounds the heart respectively – following vaccination with mRNA COVID-19 vaccines Pfizer/BioNTech and Moderna.

Symptoms after vaccination include chest pain, shortness of breath and palpitations.

DSRU’s research found that events were very rare, and most cases were mild with vaccinees making a full recovery.

But DSRU’s review echoes previous findings that men and people under 30 are more likely to experience myocarditis and pericarditis after an mRNA COVID-19 vaccine.

So far, only data from spontaneous reporting – whereby healthcare professionals and patients report side effects – are available. This means cases may be missed, or misdiagnosed and there is little extra information to help researchers and doctors understand who is more at risk. In addition, it’s not possible to gauge incidence rates of these events by relying exclusively on spontaneous reporting.

Only mRNA vaccines have been approved for use in children older than 12, so as vaccination programmes around the world progress into younger age groups, rates of myocarditis and pericarditis need to be monitored.

Professor Saad Shakir, who led the DSRU study, said: “Our review shows a similar picture across the UK, Europe and America and confirms these are very rare adverse events. But very, very occasionally they are serious.

“All we have is passive spontaneously reported information at the moment, which is very good for detecting signals but, like all pharmacovigilance methods, has limitations. With proactive research, we can understand who is at greater risk and why. And we can introduce measures to protect them.”

DSRU researchers studied spontaneous reports from the UK, America and Europe to estimate the frequency of myocarditis and pericarditis following COVID-19 vaccines by Pfizer/BioNTech and Moderna.

In the UK, as of August 4, 2021, there were 165 reported myocarditis events and 140 pericarditis events after the Pfizer/BioNTech Covid-19 vaccine. Two of these events were fatal.

This equates to approximately 7.93 cases of myocarditis and 6.73 cases of pericarditis per million vaccinees who had received at least one dose of the Pfizer/ BioNTech vaccine.

Among vaccinees who received the Moderna vaccine, there were 29 reports of myocarditis and 25 reports of pericarditis. None were fatal. This equates to 2.07 cases of myocarditis and 1.79 cases of pericarditis per million vaccinees.

Data from the US and Europe shows events were more common in men and people aged under 30. Events appear to occur within a few days of vaccination and are more common after a second mRNA vaccine dose.

Myocarditis is more common in men generally. It has also been observed as a side effect following other vaccinations, including for smallpox, influenza, and hepatitis B vaccines.

DSRU’s review is published as a pre-print this week (16/9/21) on MedRxiv.