Dr. Anthony Fauci, the United States' top infectious diseases expert, labeled it "a liberating feeling" to base his statements on science without fear of condemnation now that a new president is in charge, reports quoted him as saying Friday.

"The idea that you could get up here, talk about what you know... and let the science speak, is a liberating feeling," Fauci said during the second daily media briefing of the President Joe Biden's administration.

Trump often questioned the recommendations of his own health counselors and science experts, at times putting more focus on vaccines like hydroxychloroquine and forcing Fauci to either publicly rebut the president or just remain quiet.

Fauci said he took no pleasure in being in a situation of refuting Trump. As the long-time chief of the National Institute of Allergy and Infectious Diseases, Fauci had been part of the former president's pandemic task force, but as the crisis dragged on he found himself contradicting Trump's falsehoods and exaggerations.

While the doctor at first appeared alongside his boss regularly during White House COVID task force briefings, Fauci was later sidelined after disputing some of Trump's baseless assertions.

Trump went on to bash Fauci publicly, even calling him and other health experts as "idiots" during a campaign sortie in the run-up to the November election.

Biden, during his election campaign, promised to make Fauci his chief medical adviser when he becomes president and the 80-year-old doctor was immediately in action: on Thursday morning, he represented the new administration through video call at a World Health Organization virtual meeting.

In the afternoon, Fauci stood alongside the President and Vice President Kamala Harris in the White House as they presented a host of executive orders aimed at reducing the spread of COVID, which is claiming the lives of more than 4,000 Americans a day.

Meanwhile, the U.S. intends to be part of the COVAX vaccine program that aims to deliver COVID vaccines to marginalized nations, Fauci told the WHO on Thursday, a day after Biden was sworn into office.

WHO chief Tedros Adhanom Ghebreyesus welcomed the U.S. decision.