"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.

The U.S. Department of Health and Human Services (HHS) said on Tuesday that it will start winding down mRNA vaccine development efforts under a federal health agency focused on developing medical countermeasures to address public health emergencies.

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."