Heart inflammation after vaccine: how many cases have there been for each type of vaccine?

The Centers for Disease Control and Prevention (CDC) is looking into reports that certain demographics are more likely to experience heart problems after receiving an mRNA covid-19 vaccine.

There are above average instances of myocarditis in adolescents and young adults, who have only recently become eligible to receive the shots. The condition is essentially an inflammation of the heart muscle and can also be caused by various viral or bacterial infections.

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The CDC is investigating the cases but has not yet established a causal link between the vaccines and myocarditis. The vaccine safety group have reiterated that there have been “relatively few” cases, and that the rate of reported cases among vaccinated young people is still less than that of the general population.

How many instances of heart inflammation have there been in vaccine recipients?

The two vaccines approved for use in the US that use the mRNA technology are those produced by Moderna and Pfizer/BioNTech. The US Vaccine Adverse Event Reporting System (VAERS) found that more than half of the cases of heart inflammation were seen in people aged between 12 and 24.

However that group only accounted for around 9% of the total doses administered so far. Speaking about those figures Dr Tom Shimabukuro, deputy director of the CDC's Immunization Safety Office, admitted: "We clearly have an imbalance there.”

VAERS data shows that there were 283 reported cases of heart inflammation amongst 16 to 24-year-olds who had received a second dose of an mRNA vaccination. Scientists would normally expect to see between 10 and 102 cases in that age group over the same time period.

Of the reported cases of myocarditis in vaccinated young people, roughly 80% were found in men.

Will this news impact the ongoing vaccine rollout?

There has been understandable caution after this news with the CDC and the vaccine manufacturers taking the relatively small number of cases very seriously. VAERS will continue to study the data and Pfizer have released a statement saying they support the CDC’s continued assessment of the heart inflammation link.

However they point out that "the number of reports is small given the number of doses administered.” Across the US around 130 million people has already received both doses of either the Pfizer/BioNTech and Moderna vaccines.

The statement continues: "It is important to understand that a careful assessment of the reports is ongoing and it has not been concluded that the mRNA COVID-19 vaccines cause myocarditis or pericarditis.”

Moderna have also made clear that a causal link has not yet been proved and that they will continue to collaborate with public health and regulatory authorities to establish whether or not it is an issue.