Updated July 31, 2022 at 1:09 PM ET
President Biden continues to feel well after testing positive for COVID-19 again in a rebound case, according to his physician, Dr. Kevin O'Connor.
As of Sunday morning, Biden's antigen testing "unsurprisingly" remains positive, the doctor said in a letter released by the White House.
"The President will continue his strict isolation measures," O'Connor said.
Biden's doctor reported on Saturday that antigen testing showed the president was positive for COVID-19, after having tested negative all four days prior to that.
On Saturday, O'Connor said Biden was not experiencing symptoms, and felt well. The doctor said there was no reason to reinitiate treatment with Paxlovid, but the president would "reinitiate strict isolation procedures."
Biden wrote on Twitter: "Folks, today I tested positive for COVID again. This happens with a small minority of folks. I've got no symptoms but I am going to isolate for the safety of everyone around me. I'm still at work, and will be back on the road soon."
Biden, 79, is fully vaccinated and has had two booster shots. He first tested positive on July 21.
He was treated with a five-day course of Paxlovid, an antiviral pill that's been found to be highly effective at reducing the risks of hospitalization and death for COVID-19 patients with mild or moderate symptoms. But some people who take Paxlovid experience a "rebound," where a person can once again test positive between two and eight days after symptoms have faded and having tested negative.
"Limited information currently available from case reports suggests that persons treated with Paxlovid who experience COVID-19 rebound have had mild illness; there are no reports of severe disease," the Centers for Disease Control and Prevention said about the phenomenon.
Copyright 2022 NPR. To see more, visit https://www.npr.org.