Joe Biden has tested positive for Covid-19 only days after testing negative and having apparently largely shrugged off an infection with the virus, the White House physician said in a statement. The president had contracted Covid and apparently recovered. But Biden had been taking the medication Paxlovid, which has reported numerous cases of effectively reducing the viral load of Covid only for it to return once the medication is stopped. The White House physician, Dr Kevin O’Connor, said in a letter that Biden “has experienced no re-emergence of symptoms, and continues to feel quite well”. In accordance with Centers for Disease Control and Prevention guidelines, Biden will re-enter 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, initially tested positive last Thursday and his health and advanced age, which had long been a subject of speculation, came to dominate the news, especially as a raspy-voiced Biden worked through his symptoms. 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. 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 Biden 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, the 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.” Paxlovid has been proven to significantly reduce severe disease and death among those most vulnerable to Covid. US health officials have encouraged those who test positive to consult their doctors or pharmacists to see if they should be prescribed the treatment, despite the rebound risk. Biden is fully vaccinated, after getting two doses of the Pfizer coronavirus vaccine shortly before taking office, a first booster shot in September and an additional dose 30 March. The new positive test jeopardizes a Tuesday trip to Michigan. Biden had planned to tout the recent passage of legislation to boost the semiconductor industry, which the White House announced earlier Saturday.