President Joe Biden removes his face mask prior to receiving his coronavirus disease (COVID-19) booster vaccination in the Eisenhower Executive Office Building's South Court Auditorium at the White House in Washington, U.S., September 27, 2021.
President Joe Biden removes his face mask prior to receiving his coronavirus disease (COVID-19) booster vaccination in the Eisenhower Executive Office Building's South Court Auditorium at the White House in Washington, U.S., September 27, 2021. Reuters / Kevin Lamarque

U.S. President Joe Biden tested positive for COVID-19 on Monday "as could be anticipated," his physician said in a memo released by the White House, adding that the president continued to feel well and would continue his isolation measures.

"He will continue to conduct the business of the American people from the Executive Residence," Dr. Kevin O'Connor wrote.

After having tested negative on Tuesday and Wednesday, Biden tested positive for COVID again on Saturday in what O'Connor described as a "rebound" case seen in a small percentage of patients who take the antiviral drug Paxlovid.

Paxlovid is an antiviral medication from Pfizer Inc that is used to treat high-risk patients, such as older patients.

Biden tweeted about his positive case on Saturday, saying it could happen to a "small minority of folks." He later posted a video on Twitter where he said he was "feeling fine" and "everything's good."

Biden's return to isolation came after he celebrated being able to work in person again at a Rose Garden event on Wednesday.

(Reporting Katharine Jackson; Editing by Doina Chiacu and Chris Gallagher)