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.

Federal regulators have asked Novavax to complete an additional clinical trial on its COVID-19 vaccine after previously delaying approval, the Wall Street Journal reported on Friday, citing people familiar with the matter.

The company says its vaccine is on track for full approval, following delay. Novavax shares soared following the announcement.