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Recent reports of heart inflammation in young men after mRNA COVID-19 vaccinations may have some parents and youth considering how – or whether – to proceed with getting their shot.

These cases, though rare, present a new complication for those who are weighing the potential risks of vaccine side effects against the risk of contracting COVID-19. Meanwhile, the drive to get as many Canadians, including young people, fully vaccinated has become all the more urgent as the threat of a highly infectious Delta variant grows.

The Globe asked experts to explain the issue and provide guidance.

What is the concern?

Officials in the U.S. and Israel have reported cases of myocarditis and pericarditis, particularly among young men around age 16 to 24, following a second dose of mRNA vaccines, which are produced by Pfizer or Moderna. Myocarditis is an inflammation of the heart muscle, and pericarditis is an inflammation of the lining outside the heart.

But it’s still unclear whether these conditions are related to the vaccine, or a coincidence.

The U.S. Centres for Disease Control and Prevention (CDC) is scheduled to discuss this matter in a meeting June 18.

Meanwhile in Canada, health officials have said the number of cases of these conditions after vaccination has been small. Health Canada and the Public Health Agency of Canada say they are monitoring reports of cases. And health authorities continue to encourage people to get immunized as soon as possible.

To ensure stronger protection against variants of concern, including the highly infectious Delta variant, “those who are eligible are urged to get fully vaccinated, including getting the second dose of a two-dose COVID-19 vaccine series,” Canada’s Chief Public Health Officer, Theresa Tam, said in a statement Wednesday.

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How many cases have been reported in Canada?

Very few so far. According to the latest national data, there were 35 reported cases of myocarditis and pericarditis following a COVID-19 vaccination in the country, up to and including June 4.

Unlike international reports, the cases in Canada have been fairly evenly split between men and women, with 19 females and 16 males, and the median age was 51 years for women and 40 years for men. Also unlike reports in the U.S. and Israel where these conditions appeared higher after the second dose, Canadian data showed 22 reported cases were after a first dose of vaccine and 11 were after the second dose. (The dose for the other two cases was not specified.)

In a more recent report, Public Health Ontario’s summary of adverse health incidents following immunization showed there were three cases in people under 18 in the province as of June 5.

How serious are myocarditis and pericarditis?

Generally, pericarditis is fairly benign, while myocarditis is a more serious condition, said Gavin Oudit, a professor in the department of medicine at the University of Alberta and clinician-scientist at the Mazankowski Alberta Heart Institute.

“But they typically happen all the time, and it’s often seasonal,” Dr. Oudit said, explaining the conditions can be caused by many different kinds of viruses, including seasonal ones.

Almost all of the cases reported after COVID-19 vaccination have been mild, and most have resolved on their own, or after treatment with anti-inflammatory medications or steroids, Dr. Oudit said.

In the CDC data, 81 per cent of the 221 patients whose recovery status was known recovered fully from their symptoms. The other 19 per cent included patients with ongoing signs or symptoms.

Why do these cases seem to be more prevalent among young men?

Experts don’t yet know. Nor are there any definitive answers yet as to why the cases are higher after a second dose.

It might be a reflection of a general pattern, since myocarditis generally seems to be more common in younger age groups and in males, said Karina Top, a pediatric infectious-disease specialist at the IWK Health Centre in Halifax and investigator at the Canadian Center for Vaccinology.

Young people tend to have a stronger immune response than older age groups, Dr. Oudit noted. And women tend to have a different immune response to viral infections than men, which may explain why these cases are higher in young men, he said.

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What are the signs to look out for?

In reports from the U.S. and Israel, people have been developing symptoms such as shortness of breath, chest pain, cough, and in more severe cases, swelling in the ankles and feet, Dr. Top said, adding some may also feel light-headed. These symptoms typically start within a few days of getting a second vaccine dose.

Even though it’s the more benign of the two, pericarditis can cause worse symptoms than myocarditis, since the pericardium – or lining around the heart – has a lot of nerves, so it can be very painful, Dr. Oudit said. But it generally clears up within a week or so, he said. With both conditions, people can also experience fatigue, fever and muscle aches, he added.

While Dr. Top recommended getting checked out by a health professional if you experience any of these symptoms, Dr. Oudit suggested taking a non-steroidal anti-inflammatory drug such as ibuprofen if you don’t feel too bad and the symptoms aren’t severe. If symptoms persist for more than three or four days, however, or you start having other problems – such as worsening shortness of breath, extreme fatigue or an abnormal pulse – see your family physician, he advised.

So what should parents and young people do about second doses?

While it’s understandable these cases of myocarditis and pericarditis have sparked concern, the fact that officials have picked up on them and are responding to them is a good thing, Dr. Top said.

It’s “a sign our systems we have in place around vaccine safety are working,” she said.

It’s also important to note that COVID-19 itself has been shown to cause myocarditis in rare instances in young people, and it is also associated with multisystem inflammatory syndrome, which can involve severe inflammation of the heart and the blood vessels in the heart, she said.

Given the risks of COVID-19, and the mild nature of rare cases of myocarditis and pericarditis after vaccination, Dr. Top said it’s still recommended that young people get fully vaccinated.

“The benefits still outweigh the risks at this point in time,” she said.

According to government data, people under age 30 now account for a growing share of COVID-19 cases. Those under 19 years old make up 19 per cent of all COVID-19 cases reported as of June 11 since the start of the pandemic, tied with 20- to 29-year-olds.

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