The University of Ottawa Heart Institute has admitted at least eight people with a rare condition that may be linked to the two mRNA vaccines produced by Moderna and Pfizer-BioNTech.
The condition, myocarditis, is an inflammation of the heart muscle.
The most common symptoms are chest pain, trouble breathing and sensations of pressure on the chest. Most cases are considered mild, with the condition often going away on its own.
In the unlikely case that the inflammation affects the heart's ability to pump blood, the patient is given anti-inflammatory drugs or steroids.
"We have several new cases," said Dr. Peter Liu, scientific director of the Ottawa Heart Institute.
"And as the vaccination effort increases, we probably will see more cases."
An Ontario Public Health report shows that any sort of post-vaccine complications, however, are exceedingly rare. For every 100,000 doses administered in Ottawa, roughly 34 people report adverse events — a little more than 0.03 percent.
Caroline Quach, is the past chair of the National Advisory Committee in Immunization, said most vaccine-related reports of myocarditis involve men younger than 30 after they've received their second dose.
Vaccine benefits outweigh risks, experts urge
Men typically experience myocarditis at a higher rate than women. So far, Ontario Public Health isn't noticing that myocarditis is occurring at a higher rate in vaccinated men than what would normally occur in the general population.
While researchers don't yet know whether mRNA vaccines cause the rare condition, Quach said the timing suggests they appear to be related.
"There seems to be a temporal link between administration of the mRNA vaccines — particularly the second dose — and the development of this inflammation of the heart," she said.
"Up until now, it was a minority of cases that needed to be admitted to hospitals," Quach added. "Most of the time, we were admitting these patients for observation more than anything else."
Experts continue to stress that benefits of vaccination outweigh the risks, and Liu said all the Ottawa patients improved fairly quickly.
But he also said it's important to know about any side effects that do exist.
"Be aware of them, so that when they do occur, the individual can alert their health providers or go to the emergency department," Liu said.
An Ottawa Public Health (OPH) spokesperson said adverse reactions to the vaccine are reported to OPH and it enters the data in the provincial reporting system.