Study: Risk for myocarditis after COVID-19 vaccination among adults very low

Study: Risk for myocarditis after COVID-19 vaccination among adults very low
Heart-related side effects following COVID-19 vaccination in adults are extremely rare, according to a new study. File photo by Debbie Hill/UPI | License Photo

Oct. 4 (UPI) -- The risk for developing heart-related complications after receiving the COVID-19 vaccine among adults is very low, particularly for women, according to the authors of a study published Monday by JAMA Internal Medicine.

Of the nearly 2.3 million people age 18 and older given both doses of the two-shot vaccines from Moderna or Pfizer-BioNTech, 15 developed myocarditis, or inflammation of the heart muscle, the data showed.


All 15 cases were in men, ages 20 to 32, and all responded well to treatment, the researchers said.

In comparison, 75 cases of the ailment, which causes shortness of breath and chest pain, among other symptoms, were reported among almost 1.6 million adult study participants who did not receive the vaccines.

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"The incidence of myocarditis following COVID-19 vaccination is very low," study co-author Dr. Mingsum Lee told UPI in an email.


"It is important to weigh the risks of COVID-19 vaccines against the risk of the COVID-19 virus [and], at this time, the benefits for vaccination far outweigh the risks," said Lee, a cardiologist with the Kaiser Permanente Los Angeles Medical Center.

Usually caused by an infection, myocarditis is an inflammation of the heart muscle that can cause chest pain, shortness of breath and irregular heartbeat, as well as reduced exercise capacity, or ability to engage in normal physical activities, according to the Centers for Disease Control and Prevention.

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The complication has been linked with both two-dose COVID-19 vaccines from Moderna and Pfizer-BioNTech, which have similar formulations.

As many as 4% of teens given the Pfizer-BioNTech shot, the only one approved for that age group, have developed myocarditis, although the cases have generally been mild, based on CDC data.

For this study, Lee and her colleagues compared rates of myocarditis among nearly 2.4 million adults who received the first dose of either of the two-shot vaccines and about 2.3 million given the second dose with those of roughly 1.6 million unvaccinated adults.

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Two people in the study developed myocarditis after receiving their first dose of the COVID-19 vaccine -- a rate of 0.8 case per 1 million people -- and 13 did so after the second, for a rate of about six cases per 1 million people, the data showed.


Eight of these cases occurred in those who received the Pfizer-BioNTech vaccine and seven had been given the Moderna shot.

In the unvaccinated group, two cases of myocarditis occurred for every 1 million people, according to the researchers.

Although none of the people who developed myocarditis post-vaccination had a history of heart disease, 14 of the 15 experienced chest pains within one to five days after receiving the vaccine.

All were hospitalized, but no one developed serious complications and they were released from the hospital without requiring treatment in the intensive care unit.

"All patients with myocarditis responded well to treatment and felt better quickly [so] we continue to believe strongly that the benefits of the COVID-19 vaccine greatly outweigh the risks," said Lee, who is also a clinician researcher with Kaiser Permanente Southern California.

"Getting the COVID-19 vaccine is one of the best things people can do to protect themselves from getting or spreading COVID-19," she said.

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