WASHINGTON (AP) — Dr. Anthony Fauci is back.

He called it “liberating” Thursday to be backed by a science-friendly administration that has embraced his recommendations to battle COVID-19.

“One of the new things in this administration is, If you don’t know the answer, don’t guess,” Fauci said in one pointed observation during a White House briefing. “Just say you don’t know the answer.”

Fauci’s highly visible schedule on Thursday, the first full day of President Joe Biden’s term, underscored the new administration’s confidence in the doctor but also the urgency of the moment.

His day began with a 4 a.m. virtual meeting with officials of the World Health Organization, which is based in Switzerland, and stretched past a 4 p.m. appearance at the lectern in the White House briefing room.

The breakneck pace showcased the urgent need to combat a pandemic that has killed more than 400,000 Americans and reached its deadliest phase just as the new president comes to office.

“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,” Fauci told reporters. White House press secretary Jen Psaki had invited Fauci to take the podium first at her daily briefing.

Biden, during his presidential campaign, pledged to making Fauci his chief medical adviser when he took office, and the 80-year-old scientist was immediately in motion.

Fauci was up well before dawn Thursday for the virtual meeting with WHO, which Biden had rejoined the previous day after Trump withdrew the U.S. from the group out of anger over how it dealt with China in the early days of the pandemic. Fauci told the group that the United States would join its effort to deliver coronavirus vaccines to poor countries.

In the afternoon, the doctor stood alongside Biden and Vice President Kamala Harris in the White House as they unveiled a series of executive orders aimed at slowing the spread of the virus, which is killing more than 4,000 Americans a day, as well as bolstering the nation’s sluggish vaccine distribution program.