'I know that this news may make some people nervous.... But the benefits of vaccination continue to significantly outweigh the risks of COVID-19'
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Following the finding of a potential one in 5,000 risk of heart inflammation after a second dose of Moderna, Ontario is recommending people aged 18 to 24 be preferentially vaccinated with Pfizer — a decision made “out of an abundance of caution,” but one that could rattle confidence in COVID-19 vaccines.
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“I just want to be clear: We’ve had no fatalities whatsoever associated with this complication related to this rare side effect of this vaccine,” Dr. Kieran Moore, Ontario’s chief medical officer of health, told a media briefing Wednesday.
Moore said the decision to issue a “preferential recommendation” was ultimately his, based on a “very small but observed increase” of myocarditis, or inflammation of the heart muscle, and pericarditis, inflammation of the sac around the heart, following vaccination with Moderna compared to Pfizer in 18- to 24-year-olds, particularly among males.
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Between June and August, based on more than 96,000 second doses of Pfizer and Moderna, both mRNA vaccines, the rate of heart complications following a second dose of Moderna was one in 5,000.
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For Pfizer-BioNTech, the rate was one in 28,000 doses.
The majority of reported cases have been mild, with most people requiring an anti-inflammatory like ibuprofen or naproxen, Moore said. Of the “very small” number admitted to hospital for a blood test, cardiogram or ultrasound, most were quickly sent home, he said.
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Moore said the risk of myocarditis and other serious “events” such as abnormal heart beats, blood clots in the legs or lungs, heart attack or intracranial haemorrhage (bleeding in the brain), is 18 times higher with a COVID infection.
“I know that this news may make some people nervous and heighten concerns about receiving a COVID vaccine, and I can understand that,” Moore said. “But the benefits of vaccination continue to significantly outweigh the risks of COVID-19 illness and related, possibly severe, consequences.”
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Ontario’s recommendation takes effect immediately, but 18- to 24-year-olds can still receive Moderna, if they so choose.
Symptoms of myocarditis or pericarditis, such as chest pain, shortness of breath and rapid or abnormal heartbeat, typically start within one week of being vaccinated, and most often after the second dose. Anyone who hasn’t developed symptoms within this timeline, the province said in a release, “should feel confident that they are unlikely to develop symptoms later,” and people who had Moderna for their first dose can safely take Pfizer for their second.
Moore said he did have concerns about addressing the myocarditis risk, but “I have to build trust with the public. We have to have accountability to the public and I think the public deserves to know the facts.” Expert advisers recommended the public be told of the increased risk “of this very rare event,” he said. “And I hope the public will realize we’re trying to be as transparent as possible.”
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Last week, a University of Ottawa Heart Institute preprint study that estimated a one in 1,000 risk of post-vaccine myocarditis following vaccination with an mRNA vaccine was retracted at the request of the authors, who said incorrect data had vastly inflated the incidence. The adjusted incidence was one in 25,000 doses.
It’s not clear why the association appears higher with Moderna versus Pfizer. Moderna has a higher amount of mRNA, “and we know that some of the side effects from Moderna are more profound,” said infectious diseases specialist Dr. Isaac Bogoch. Moderna may also offer a longer-lasting immune response, he said, which, again, might be related to the amount of mRNA in Moderna versus Pfizer.
While myocarditis appears more common in males than females, and most often after the second dose, “that doesn’t mean it’s exclusively males, exclusively young and exclusively second dose,” said Bogoch, of Toronto’s University Health Network. “It can happen after the first dose in females and older, but it’s rare. It’s still a rare event.”
“You have to be transparent, you have to tell people what the risk is and you have to express uncertainty that this might change with time,” he said.
With additional reporting from The Canadian Press
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Ontario recommends Pfizer shots instead of Moderna for young adults over possible heart risks - National Post
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