COVID vaccine related myocarditis mild and self-resolving

COVID-19 vaccine-associated myocarditis has a mild and self-resolving clinical course, cardiologists from Melbourne have confirmed.

The single centre study included 33 adolescents who presented at the Monash Children’s Hospital between August and December 2021 with typical symptoms of myocarditis associated with troponin rise (> 15 ng/L) within 28 days of their first or second doses of COVID-19 mRNA vaccine.

Fourteen patients had rising troponin levels at presentation, 8 had ECG changes typical for pericarditis, but no arrhythmias were detected by inpatient telemetry. Left ventricular systolic function was normal at presentation in 29 patients and mildly impaired in four.

Findings on CMR imaging were abnormal in 27 of 32 patients, showing late gadolinium enhancement in a patchy subepicardial to transmural pattern which was especially marked in the inferolateral left ventricular free wall.

Evidence of oedema was detected in 22 of 32 patients, meeting the Lake Louise criteria for myocarditis. The right ventricular apex was affected in one patient and a trace pericardial effusion was noted in 25 of 33 patients and pericardial enhancement in two of 33 patients.

Myocarditis using CDC criteria was confirmed for 22 of 32 patients and was probable for ten of 32 patients.

All patients improved in hospital after treatment with high dose ibuprofen for one week or until symptom resolution and proton pump inhibitor therapy. The median hospital stay was 2.3 days and bed rest followed by a gradual return to normal activities was advised.

“COVID-19 mRNA vaccine-associated myocarditis has a mild, self-resolving clinical course, in contrast to reported complications and long term sequelae associated with COVID-19, such as multisystem inflammatory syndrome in children, and other forms of myocarditis,” the researchers concluded in their letter published in the MJA.

“The long term consequences of myocardial injury with vaccine-associated myocarditis nevertheless warrant further investigation,” they added.

Meanwhile, a review of more than 8,000 cases of vaccine associated myocarditis and pericarditis published in The BMJ concluded that myocarditis is rare, cases are highest among young males shortly after a second dose, and are probably higher after Moderna’s mRNA vaccine than after Pfizer’s vaccine.

The researchers also found that the risk of myocarditis or pericarditis might be lower when the second dose is given more than 30 days after the first dose.

However, they cautioned, “as the incidence of myocarditis after mRNA vaccination is a rare adverse event, the findings must be considered alongside the overall benefits of vaccination and with detailed risk-benefit analyses to support policy recommendations for optimal dosing intervals and vaccine products for different populations”.

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