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 are asking Novavax to complete an additional randomized clinical trial on its Covid-19 vaccine after previously delaying approval, people familiar with the matter said, a request that could be so prohibitively expensive the company might not be able to fulfill it.

At the peak of the COVID-19 pandemic, many vaccine skeptics turned to ivermectin, a medication proven to fight off parasitic diseases, to offer protection against the virus. As The Dispatch Fact Check reported repeatedly at the time, ivermectin has not been proven effective at either slowing the spread of COVID-19 or alleviating its symptoms.