The Trump administration's effort to impose new requirements on Novavax's COVID-19 vaccine -- the nation's only traditional protein-based option for the coronavirus -- is sowing uncertainty about updates to other vaccines too.

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.

Comments over the weekend by FDA chief Martin Makary suggest the agency views Novavax’s updated COVID shot as a “new product” requiring additional clinical study.