Vaccine myocarditis risk “far outweighed” by COVID-19 infection

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The risk of heart damage from COVID-19 infection is far greater than that from receiving a dose of the messenger RNA (mRNA) vaccine, according to the authors of a retrospective case series published in JAMA Cardiology.

Researchers from Mayo Clinic (Jacksonville, USA) examined cases of myocarditis in young men who developed symptoms shortly after receiving the second dose of the Moderna or Pfizer mRNA COVID-19 vaccines. They note that several recent studies suggest healthcare professionals should watch for hypersensitivity myocarditis as a rare adverse reaction to being vaccinated for COVID-19. However, the researchers stress that this awareness should not diminish overall confidence in vaccination during the current pandemic.

While reports of post-vaccine myocarditis in some areas are higher than baseline, the imminent and greater risk for heart damage and death continues to be from becoming infected with COVID-19, they suggest. Up to 60% of people who are seriously ill with COVID-19 experience injury to their heart, and nearly 1% of fit athletes who had a mild COVID-19 infection show myocarditis on an MRI, the researchers add.

The retrospective case series in JAMA Cardiology studied 23 men in the US military who were hospitalised with myocarditis symptoms within four days of receiving the second dose of an mRNA COVID-19 vaccine. Three of the patients previously had been infected with COVID-19, and their symptoms started after the first dose of the vaccine.

The cases occurred between January and April 2021. Sixteen had received the Moderna vaccine and seven had received the Pfizer vaccine. For context, the study’s authors add, it is important to note that the military administered more than 2.8 million doses of messenger RNA COVID-19 vaccines during that time.

All 23 military patients had symptoms of severe chest pain and significantly elevated cardiac troponin levels. Each patient rapidly recovered, which, combined with the timing and symptoms, supports the diagnosis of hypersensitivity myocarditis.

“Hypersensitivity myocarditis following vaccination is rare, with the exception of smallpox vaccine. The risk of myocarditis after receiving mRNA vaccine is far less than the risk of myocarditis following actual COVID-19 infection,” says Leslie Cooper, chair of the Department of Cardiology at Mayo Clinic Cooper is senior author of the study, which was conducted with US military medical centres.

Another observational case study recorded details of eight men between the ages of 21 and 56 who were hospitalised with chest pain and diagnosed with myocarditis by laboratory and cardiac magnetic resonance imaging (MRI). The patients developed symptoms, starting with a fever, within two to four days of receiving their second dose of a COVID-19 vaccine. One patient who had previously recovered from COVID-19 had symptoms after the first dose. All eight patients in the study recovered from the effects of myocarditis and no longer had chest pain. The findings, co-authored by Cooper with researchers from Mayo Clinic and other medical institutions in the USA and Italy, are published in Circulation.

“People of all ages should choose to get a COVID-19 vaccine because the risks are extremely low compared to the benefits. Additionally, the growing body of research shows that vaccine-associated myocarditis resolves quickly in almost all cases,” says Cooper.


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