"Based on the available data, a warning statement in the factsheets for both healthcare providers and vaccine recipients and caregivers would be warranted", FDA official Doran Fink said at the advisory committee meeting.
"It's a new vaccine, it's been increasingly elevated as a concern, and all other countries except for us have done something that errs on the side of safety", she told AFP, adding she was holding off having her 13-year-old child receive a second dose until she learns more.
The conditions are more commonly reported after the second dose with symptoms usually appearing within several days after vaccination and mainly affect male adolescents and young adults, the health units said.
During the presentation, Dr. Matt Daly - chair of the ACIP COVID-19 vaccines working group - emphasized the strength of the USA vaccine safety monitoring system.
Public Health Ontario said of the 19 reports, four were diagnosed with myocarditis, 12 were diagnosed with pericarditis and the other three were either perimyocarditis, myopericarditis or inflammatory cardiac reaction of unclear significance.
The CDC said it was still assessing the risk from the condition and did not specifically confirm a causal relationship between the vaccines and the heart issue.
Myocarditis is rare but not a new disease, he said, with the findings suggesting mRNA vaccines "may be a new trigger". Those who experienced the heart inflammation had mild symptoms which improved quickly to treatment with rest and anti-inflammatory medicine.
The new CDC hearing will dive deeper into updated data that has been independently verified, rather than being self-reported.
"Currently, the benefits still clearly outweigh the risks for COVID-19 vaccination in adolescents and young adults", reads a slide from the presentation.
Dr Christopher Blyth from the Australian Technical Advisory Group on Immunisation said there had been 60 cases suffering clotting issues from 4 million AstraZeneca vaccines administered, including two deaths.
While the extent of heart conditions among youth is now unclear, a report recently submitted to the Israeli Ministry of Health concluded the risk of developing a heart issue post-vaccine ranged from 1 in 3000 to 1 in 6000 among men aged 16 to 24. The provincial rate is 45.8 reports of AEFI per 100,000 people.
Many more primary care providers will be offered the chance to administer mRNA vaccines as the supply of Pfizer significantly increases and the first supplies of Moderna arrive in September/October.
Despite reports from Global Positioning System showing a surge in the number of patients cancelling their second Astra Zeneca dose, Chief Health Officer Paul Kelly said that most people "are going to get the second dose".
"Whether you are getting your first dose or your second dose, remember that mRNA is mRNA", he said on Wednesday.
While the case numbers are low, they are still higher than what would be expected in these age groups and researchers are studying possible biological triggers.
Pfizer, whose vaccine has been authorized for use in Americans as young as 12, previously said it had not observed a higher rate of heart inflammation than would normally be expected in the general population.
The self-serve option is open to anyone 12 years of age and older for first-dose appointments for the COVID-19 vaccine at any public clinic or pharmacy across Waterloo region.