"This is one of the greatest scientific accomplishments in history. It will save millions of lives and soon end the pandemic once and for all," Trump said at the time in a speech delivered from the Oval Office.

Adams, who served as surgeon general during the first Trump administration, said Kennedy's assertions about the efficacy of mRNA vaccines are "simply not true."

Kansas Senator Roger Marshall says he's in favor of the decision to cancel contracts and pull funding for some vaccines currently under development.