Ontario is now recommending that younger adults only be given the Pfizer vaccine due to an apparent increase in the likelihood of developing a rare heart condition following vaccination with Moderna.

The new “preferential recommendation” for the age group was issued on Wednesday following the review of data that points to a higher rate of myocarditis and pericarditis among younger adults who have received the Moderna vaccine for their second dose, particularly males.

Officials say that about one in approximately 5,000 males between the ages of 18 and 24 have developed the condition after receiving Moderna for their second dose compared to about one in 28,000 males who got Pfizer instead.

About one in 17,000 females who received Moderna for their second dose also developed myocarditis or pericarditis.

“While we are making this recommendation it is important to note that myocarditis/pericarditis remains a rare adverse event following immunization, even amongst the age groups with the highest observed rates,” Chief Medical Officer of Health Dr. Kieran Moore said during a briefing on Wednesday afternoon.

“The majority of reported cases have been mild with individuals recovering quickly normally with anti-inflammatory medication, such as Ibuprofen.”

The Ministry of Health says that those between the ages of 18 and 24 will still be able to receive the Moderna vaccine with “informed consent” however the default will now be to administer Pfizer to that age group.

During his news conference, Moore conceded that the new recommendation “may make some people nervous” and contribute to “heightened concerns about receiving COVID vaccines” but he said that it is important to remember that individuals who contract COVID-19 are 18 times more likely to develop inflammatory heart conditions like myocarditis.

“I have three young boys, two of whom are in the 20 to 24-year-old age group and they both received Moderna and I had no concerns about them having that product,” he said. “Moderna is an excellent product, it's got very good immune uptake and it's gotten very good prolonged immune response and protection. I have complete confidence in it.”

Speaking on background during a technical briefing on Wednesday, officials with the ministry said there have been fewer than 10 instances of individuals being admitted to intensive care after developing myocarditis or pericarditis post vaccination and no fatalities.

Moore also pointed out that many of the people who have been admitted to intensive care after developing a vaccine-induced case of myocarditis have been discharged a few days after admission once the condition was confirmed through testing.

“It is a very small number of people that have had to be admitted to the intensive care unit and most of the time that's for investigation so taking a blood test, a cardiogram or an ultrasound and then they're been rapidly discharged home,” he said.

Myocarditis involves the inflammation of a heart muscle while pericarditis involves the inflammation of the thin layer of skin surrounding the heart. The more common symptoms associated with the condition include chest pain, shortness of breath, an irregular heart rate and fatigue.