Myocarditis is the name given to inflammation of the heart muscles, or “myocardium”. The condition—which typically results from viral infection—can serve to reduce the heart’s ability to pump blood and result in the development of a rapid or irregular heart rhythm. It often occurs in association with pericarditis, an inflammation of the fibrous sac that surrounds the heart that can trigger sharp chest pain, shortness of breath and palpitations.
Various reports from Canada, Israel and the US have indicated that there may be an increased risk of myocarditis following the administration of mRNA vaccinations against SARS-CoV-2, the virus that causes COVID-19.
Furthermore, preliminary data from studies in Canada and France have suggested that myocarditis incidence rates may be higher following the Moderna vaccine than the BioNTech/Pfizer jab.
The Centers For Disease Control and Prevention (CDC) has already asserted that people infected with COVID-19 have a greater risk of myocarditis and other inflammatory heart conditions than those vaccinated against the disease.
And the UK Health Security Agency (UKHSA) has advised that cases of myocarditis and pericarditis are “very rare following vaccination” and usually present as “mild or stable” cases, with patients typically recovering fully without medical treatment.
To investigate further, epidemiologist Professor Rickard Ljung of the Swedish Medical Products Agency and his colleagues studied health data on a total of some 23.1 million people from Denmark, Finland, Norway and Sweden from late December 2020 to early October 2021.
The team looked for incidences of myocarditis and pericarditis and, for each case, considered the subject’s sex, age and vaccination specifics.
They focused in particular on cases where the inflammatory heart conditions developed within 28 days of either an initial or second vaccination shot.
By the end of the study period, the researchers reported, 81 percent of the subjects had been vaccinated.
READ MORE: Next pandemic ‘not if, but when’ as wet markets STILL a threat
The researchers wrote: “Results of this large cohort study indicated that both first and second doses of mRNA vaccines were associated with increased risk of myocarditis and pericarditis.
“For individuals receiving two doses of the same vaccine, risk of myocarditis was highest among young males after the second dose.
“These findings are compatible with between 4 and 7 excess events in 28 days per 100,000 vaccinees after BNT162b2 [the BioNTech/Pfizer vaccine]and between 9 and 28 excess events per 100,000 vaccinated after mRNA-1273 [the Moderna vaccine].”
They concluded: “This risk should be balanced against the benefits of protecting against severe COVID-19 disease.”
The full findings of the study were published in the journal JAMACardiology.