The Washington Post cited "informed" sources that US health officials are reviewing reports which indicate that the Moderna vaccine against COVID-19 may be linked to a higher risk of rare heart disease in young adults than previously thought.

The newspaper's report mentioned that the investigation is focused on data from Canada which suggests that young people, especially males “below the age of 30 or so” who received the Moderna vaccine are at a higher risk of myocarditis than those who received the Pfizer vaccine.

The Post also quoted a source as saying, "It is still too early for regulators to reach a conclusion, and more work is needed before any recommendation can be made."

On its part, the FDA said, “We will not comment on internal meetings or discussions, but we can say that the FDA is fully committed to reviewing data when it is available to it.”

Moderna has not commented on the matter, according to Reuters. 

The potential review comes just two days after US health officials announced that a third booster dose would be available to Americans starting Sept. 20. This comes out of fears that the protection provided by the primary vaccines is less than what is required in the face of the increasing infections with the mutated strain known as Delta.

And last June, the FDA issued a warning that a “likely association” had been found between the vaccines, Moderna and Pfizer, and rare occurrences of myocarditis and pericarditis, especially after receiving the second dose of Moderna in young people. The reason is that vaccine consultants in the US Centers for Disease Control and Prevention (CDC) received about 1,200 reports of heart inflammation after 300 million doses of the two vaccines.