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.

Novavax's COVID vaccine was approved under an emergency use authorization in August 2022, and the company has pursued full licensing with the Food and Drug Administration (FDA), which gave the company a decision date of April 1 based on the Prescription Drug User Fee Act.