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Individuals who received Moderna as a first dose can safely take the Pfizer/BioNTech vaccine as a second dose, the province said, noting that two mRNA doses offer the best protection against COVID-19, regardless of brand.

Tijana Martin/The Globe and Mail

Ontario is recommending that males 18-24 receive the Pfizer/BioNTech COVID-19 vaccine going forward because of the rare risk of heart inflammation linked to the Moderna vaccine.

The change, announced Wednesday, comes after Ontario’s children’s vaccine table and other officials analyzed adverse event reports. They found a slightly increased risk of myocarditis and pericarditis in males 18-24 after administration of the Moderna vaccine. Myocarditis is inflammation of the heart muscle and pericarditis is inflammation of the membrane around the heart.

The risk is about one in 5,000 in males aged 18-24 who received Moderna, and symptoms typically occur within a week of the second dose, the province said.

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Individuals who received Moderna as a first dose can safely take the Pfizer/BioNTech vaccine as a second dose, the province said, noting that two mRNA doses offer the best protection against COVID-19, regardless of brand.

Isaac Bogoch, an infectious diseases physician at Toronto’s University Health Network, said the decision to recommend the Pfizer/BioNTech vaccine over Moderna’s is a smart move.

“If you’ve got no issues with supply and if you’ve got a clear indicator that one vaccine has a lower incidence of a rare adverse effect than another one, then you should preferentially use that vaccine. It’s as simple as that,” Dr. Bogoch said.

The vast majority of cases of heart inflammation linked to COVID-19 mRNA vaccines are mild and resolve with anti-inflammatory medication. A small number of individuals have been hospitalized as a result of heart inflammation after vaccination in Ontario and no deaths have been reported, according to the province. The rates are similar to what’s been reported in other countries.

Anyone who received the Moderna vaccine should feel assured they did the right thing, the province said. If more than a week has passed since vaccination and no symptoms have appeared, it’s unlikely the individual will experience heart inflammation.

Unvaccinated individuals face a much higher likelihood of developing heart inflammation as a result of COVID-19 infections, health officials said, and the risk of severe illness and other complications is also much greater.

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