President Joe Biden tested positive for COVID-19 again Saturday, slightly more than three days after he was cleared to exit coronavirus isolation, the White House said, in a rare case of “rebound” following treatment with an anti-viral drug. Biden tweeted about his positive case, saying it can happen to 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," he tweeted. White House physician Dr. Kevin OConnor said in a letter that Biden “has experienced no reemergence of symptoms, and continues to feel quite well.” In accordance with Centers for Disease Control and Prevention guidelines, Biden will reenter isolation for least five days. The agency says most rebound cases remain mild and that severe disease during that period has not been reported. Biden, 79, was treated with the anti-viral drug Paxlovid, and tested negative for the virus on Tuesday and Wednesday. He was then cleared to leave isolation while wearing a mask indoors. His positive tests puts him among the minority of those prescribed the drug to experience a rebound case of the virus. While Biden was testing negative, he returned to holding in-person indoor events and meetings with staff at the White House and was wearing a mask, in accordance with CDC guidelines. But the president removed his mask indoors when delivering remarks on Thursday and during a meeting with CEOs on the White House complex. Asked why Biden appeared to be breaching CDC protocols, press secretary Karine Jean-Pierre said, “They were socially distanced. They were far enough apart. So we made it safe for them to be together, to be on that stage.” Regulators are still studying the prevalence and virulence of rebound cases, but the CDC in May warned doctors that it has been reported to occur within two days to eight days after initially testing negative for the virus. Word of Biden’s positive test came just two hours after the White House announced a presidential visit to Michigan this coming Tuesday to highlight the passage of a bill to promote domestic high-tech manufacturing.