A Canadian study suggests cases of heart muscle inflammation related to COVID-19 mRNA vaccines are rare but higher than expected among young men who got a second dose of
Lead author Dr.
He said the study bolsters previous research elsewhere with more robust data, which is based on hospitalizations, emergency room visits and lab tests in
The study, published this week in the
About seven million doses of
Researchers identified 99 cases of myocarditis among a total of 10.2 million doses that were administered. They expected to see about seven cases, most of them among females, based on what would have been typical. Instead, the study showed 80 males developed myocarditis, and 19 females.
Most cases were among men and after the second dose. On average, the males were younger than females, age 28 versus 45 among cases within seven days, and age 31 versus age 49 among cases within 21 days.
Out of 100,000 second doses of
However, seven days after a third dose of
Cases of myocarditis are typically mild for young men who seek medical help for chest pain following vaccination, Janjua said, adding treatment involves monitoring of symptoms, sometimes in hospital, as their condition may resolve with or without medication.
"When I say mild, I mean self-resolving. So, these were people who had illness for one or two days, or three days, and then they recovered. When we compare that with a COVID infection-related myocarditis, we see that (condition) stays for a very long time, that for 10 to 12 days people were admitted to hospital."
Symptoms can include chest pain, shortness of breath or a rapid or abnormal heart rhythm.
Myocarditis can occur for various reasons, he said, including a viral infection like the flu, for example, typically among older people.
"We don't expect any residual effects given the mildness of illness," Janjua said of myocarditis involving mRNA vaccines administered to young men, who are otherwise not susceptible to the condition.
Authors of the study say they support the use of
For booster shots, NACI said in a statement that
Earlier this month, the agency said there is currently no evidence to suggest any meaningful difference in protection between different bivalent booster vaccines targeting the original COVID-19 strain and the Omicron subvariant, "nor any clinical trials directly comparing the
Authors of the
Janjua, who is also a clinical professor at the
"
Cases of post-COVID-19 vaccination linked with myocarditis and pericarditis, inflammation of the two-layered sac surrounding the heart, have been reported internationally since 2021 among males as young as 12, prompting ongoing research.
A study published in January in the
For men aged 18 to 24, it reported 56 cases per million doses after the
Janjua said researchers elsewhere are trying to determine why males face a higher risk of myocarditis linked to COVID-19 mRNA vaccines compared with females, but hormonal differences related to immunity are believed to be a factor.
While most cases have been mild and resolved quickly, the
Overall, Janjua said the risk of complications from a COVID-19 infection is much higher than developing myocarditis from a
"Go with whatever is available to reduce your risk of getting infected."
This report by The Canadian Press was first published
This story was produced with financial assistance from the
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