The US Food and Drug Administration has discussed with vaccine-maker Novavax the need for an additional trial of its Covid-19 vaccine as a post-approval commitment, a source familiar with the matter told CNN.

Novavax has been available since 2022 through a pandemic-era Emergency Use Authorization. A decision on full approval – which rival mRNA shots from Moderna and Pfizer and its partner BioNTech already have - was due from the Food and Drug Administration by April 1, but had been delayed by the FDA without explanation.

A new randomized study could cost Novavax tens of millions of dollars, vaccine experts say