Having been rather sidelined by Mr Biden's predecessor Donald Trump, Dr Anthony Fauci took to the podium during a White House briefing, a return to the spotlight that underscored the new administration’s confidence in the doctor.
Dr Fauci's highly-visible schedule on Mr Biden's first full day in office also highlighted the crisis the US faces as Covid-related deaths topped 400,000.
Dr Fauci did not mention Mr Trump by name, but he made it clear he believed the new administration would not trade in the mixed messages of its predecessor.
“The idea that you can get up here and talk about what you know and what the science is… it is something of a liberating feeling,” Dr Fauci told reporters.
Dr Fauci insisted that he always spoke the truth and took “no pleasure” in having to contradict the president, a move that often drew Mr Trump’s wrath.
While choosing his words carefully, Dr Fauci acknowledged that it had been difficult at times to work for Mr Trump, who repeatedly played down the severity of the pandemic, refused to consistently promote mask-wearing and often touted unproven scientific remedies, including a malaria drug and even injecting disinfectant.
“It was very clear that there were things that were said, be it regarding things like hydroxychloroquine and other things, that really was uncomfortable because they were not based in scientific fact,” Dr Fauci said.
During his presidential campaign, Mr Biden pledged to make Dr Fauci his chief medical adviser when he took office.
Eighty-year-old Dr Fauci was up well before dawn on Thursday for a virtual meeting with the World Health Organization which Mr Biden had rejoined the previous day after Mr Trump withdrew the US from the group out of anger over how it dealt with China in the early days of the pandemic.
Dr Fauci told the group that the United States would join its effort to deliver coronavirus vaccines to poor countries.
White House press secretary Jen Psaki had invited Dr Fauci to take the podium first at her daily briefing.
In his return to the briefing room, Dr Fauci joked with reporters, seemingly far more relaxed than at any point last year.
“One of the new things in this administration is, If you don’t know the answer, don’t guess,” Dr Fauci said in one pointed observation during the White House briefing.
“Just say you don’t know the answer.”
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