For every one million Americans immunized with a coronavirus vaccine, about 60 develop temporary heart problems, according to a study published Wednesday in JAMA magazine.
The complications were all short-lived, the researchers found. And these heart problems are far more common in patients who develop Covid-19, as external experts have found.
When analyzing the medical records of just over 2 million people who had received at least one dose of a coronavirus vaccine by May 2021, the new study found 20 cases of myocarditis, or inflammation of the heart muscle, and 37 cases of pericarditis, an inflammation of the heart muscle membrane that surrounds the heart.
Patients who were admitted to the hospital were discharged after just a few days, none of them died.
The incidence of myocarditis in the study is 10 cases per million vaccinated, higher than the Centers for Disease Control and Prevention’s estimate of 4.8 cases per million, suggesting there may be more cases than the federal database tracking these Side effects mentioned after vaccinations.
“We see that these adverse events lead to very short and inconspicuous hospital stays,” said Dr. Jeremy Faust, an emergency doctor at Brigham and Women’s Hospital in Boston who was not involved in the study. “The same cannot be said so far of hospital stays for Covid-19 in this or any other age group.”
“When people are hospitalized for Covid, the consequences are far more severe,” added Dr. Faust added, who compared post-vaccination myocarditis rates with those in Covid-19 patients.
The researchers worked with the Providence Health System to evaluate medical records from 40 hospitals in Washington, Oregon, Montana and Los Angeles County, California.
They found that myocarditis developed a median 3.5 days after vaccination, mostly after the second dose and in people with a median age of 36 years. Three quarters of the 20 cases were men.
The 19 patients admitted to the hospital were discharged after a median of two days. About three weeks after vaccination, 13 patients had recovered from their symptoms and the remaining seven improved.
Pericarditis affected elderly patients, a mean age of 59 years and later, about 20 days after vaccination, the researchers found. Pericarditis was also more common in men. Of the 37 identified cases, 13 were hospitalized; the average stay was one day.
A separate study published online last week found that the incidence of myocarditis in boys ages 12 to 17 with Covid-19 was 876 per million; in girls of the same age group with Covid-19, the incidence was 213 cases per million.
The study has not yet been peer-reviewed or published in a scientific journal.