WASHINGTON (AP) — President Joe Biden has tested positive for COVID-19 for the second straight day, in what appears to be a rare case of “rebound” following treatment with an anti-viral drug. White House physician Dr. Kevin O’Connor says in a letter Sunday that the president “continues to feel well” and will keep on working from the executive residence. After Biden tested positive on Saturday, he canceled upcoming plans to travel and hold in-person events. He’s isolating for at least five days in accordance with Centers for Disease Control and Prevention guidelines. The 79-year-old Biden first tested positive on July 21. He was treated with the anti-viral drug Paxlovid and he had ended his isolation on Wednesday.