View of a vial of the Moderna vaccine against COVID-19 at the National Secretary of Sports vaccination centre in Asuncion, Paraguay on June 19, 2021. Photo: AFP

The committee, hosted by the Centers for Disease Control and Prevention (CDC), will hear a risk-benefit analysis as researchers explore whether the shots can cause myocarditis, as well as cases of inflammation of the heart lining, pericarditis. 

Israel first was the first country to identify a possible link.

"These cases are rare, and the vast majority have fully resolved with rest and supportive care," said CDC director Rochelle Walensky last week ahead of the meeting, which was initially scheduled for last Friday but postponed because of a new public holiday.

The cases that have been confirmed were investigated following initial reports to vaccine safety monitoring systems, and come from more than 20 million adolescents and young adults that have been vaccinated, added Walensky.

While 300 out of 20 million is a small number, it is still likely higher than what would otherwise be expected for the age group.

A previous meeting on the issue convened on June 10 by the Food and Drug Administration heard that most of the cases were among young men and occurred within a week of the second dose.