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.

The President Donald Trump administration's request for Novavax Inc. to conduct new clinical trials for its COVID-19 vaccine has created uncertainty across the vaccine industry, potentially affecting other manufacturers.