WASHINGTON — President Joe Biden tested positive again for COVID-19 in a so-called “rebound” case seen in people who take the antiviral drug Paxlovid.

Biden, 79, isn’t experiencing symptoms after getting a positive rapid test on Saturday morning, but will resume isolation at the White House, his physician Kevin O’Connor said in a letter released by the White House.

The test once again disrupted Biden’s schedule after he resumed in-person events this past week. Trips ton Sunday to his hometown of Wilmington, Del., and on Tuesday to Michigan to celebrate the passage of a bill to subsidize U.S. semiconductor production were canceled, according to the White House.

“I’m feeling fine, everything’s good,” Biden said in a video posted Saturday to his Twitter account that showed him without a face mask on a balcony. He said he’ll work from home “for the next couple days.”

The president “has experienced no reemergence of symptoms and continues to feel quite well” and “there is no reason to resume treatment at this time, but we will obviously continue close observation,” O’Connor wrote.

The Centers for Disease Control and Prevention recommend that people who test positive again after receiving Pfizer Inc.’s Paxlovid treatment isolate for at least five days.

Biden took Paxlovid, a five-day treatment course that has been shown to sharply reduce symptoms, after first testing positive on June 21. He concluded the drug therapy Monday evening and tested negative each of the four days after that.

A small percentage of COVID patients who take Paxlovid later test positive in rebound cases, like Biden, which are typically associated with few or no symptoms.

When Biden resumed in-person public events this past week after testing negative, he flouted CDC guidance saying that people recovering from COVID should continue wearing a mask for 10 days following the onset of symptoms.

The president attended an economic briefing indoors on Thursday with Treasury Secretary Janet Yellen, Commerce Secretary Gina Raimondo, Council of Economic Advisers Chairwoman Cecilia Rouse and several other White House aides, in addition to Marriott International Inc. CEO Tony Capuano. Biden entered the room with a mask but then took it off and shook hands with several participants. He later sat at a desk that was distanced from others.

“They were socially distanced, they were far enough apart, so we made it safe for them to be together,” White House Press Secretary Karine Jean-Pierre said Thursday when asked why Biden went maskless at the event.

CDC guidelines don’t say that social distancing is a criterion for allowing people who recently tested negative to be maskless in public settings.