November 22, 2022 – The overall risk of developing myocarditis after a COVID-19 vaccination remains rare, according to New study Posted in Canadian Medical Association Journal.
At the same time, myocarditis appears to be more common in men ages 18 to 29 who receive the Moderna shot. The researchers recommended the Pfizer syringe for this group.
says Naveed Janjua, MBBS, senior author of the study and executive director of Data and Analysis Services at the British Columbia Center for Disease Control.
However, the number of people who develop myocarditis after vaccination is “three to six times what we see after COVID,” says C. Buddy Krish, director of the Vanderbilt Vaccine Research Program. Krish, who was not involved in this study, has led clinical trials of the COVID-19 vaccine throughout the pandemic.
Janjua and colleagues looked at data from people in British Columbia who were vaccinated against COVID-19 from December 2020 to March 2022. They looked for hospital admissions or emergency department visits for myocarditis, or inflammation of the heart (myocarditis).Cyst-like inflammation of the tissues pericardium) during 7-21 days after vaccination. The research team also compared the number of cases observed with the cases expected if there was no association between the COVID-19 vaccine and myocarditis.
Overall, more than 10.2 million doses of Pfizer’s or Moderna’s vaccines have been administered to people 12 or older in BC over that time, including nearly 7 million doses from Pfizer and 3.2 million doses from Moderna. It was about 4 million first doses, about 3.9 million second doses, and 2.3 million third doses.
The researchers found 99 cases of myocarditis within 7 days after vaccination, compared to an expected seven. The incidence of myocarditis was 0.97 cases per 100,000 vaccine doses, compared to the expected rate of 0.23 per 100,000 population. The observed rate was about 15 times higher than expected.
They also found 141 cases within 21 days, compared to an expected 20. The incidence of myocarditis was 1.37 cases per 100,000 vaccine doses, compared to the expected rate of 0.39 per 100,000 population. The observed rate was about 7 times higher than expected.
When analyzed by age, the incidence of myocarditis was highest between ages 12-17 and 18-29, and lowest among ages 70-79. By sex, the incidence of myocarditis was higher in men than in women.
“The numbers are small [for Moderna versus Pfizer]and so it may not be entirely accurate, but that was a common theme,” Krish says. “This may be due to the slightly higher amount of antigen in Moderna’s vaccine compared to Pfizer’s.”
Krish said the study confirmed what other researchers in the United States and around the world were seeing.
“At the end of the day, the absolute number of cases of post-vaccination myocarditis is very low, although it is higher than we would expect. Pfizer and Moderna as well as the National Institutes of Health, CDC and others have all launched large-scale studies to understand why this is happening.”
Finally, says Krish, cases of post-vaccination myocarditis have been mild.
“This should provide parents with a measure of confidence as they seek to protect their families from COVID disease, including often mild cases of post-COVID myocarditis,” he adds.