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 Inc. shares fell after the Wall Street Journal reported that US regulators asked the company to conduct another clinical trial of its Covid vaccine.

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.