READ THIS NEXT: Dr. Fauci Just Gave This Concerning New Warning to Anyone Who’s Had COVID. Biden returned to work in the Oval Office on July 27 after receiving two negative COVID tests following five days of quarantine, according to CNBC. The president was expected to recover from his infection quickly, as he is fully vaccinated and twice boosted.ae0fcc31ae342fd3a1346ebb1f342fcb “My symptoms were mild, my recovery was quick, and I’m feeling great,” Biden said when he ended his isolation. On July 26, White House physician Kevin O’Connor wrote that the president’s COVID symptoms had “almost completely resolved,” and noted that Biden felt well enough to “resume his physical exercise regimen.” Just three days after ending his isolation, it was confirmed that Biden was COVID positive again on July 30, per CNN. “Folks, today I tested positive for COVID again. This happens with a small minority of folks,” Biden tweeted at the time. The reinfection was first revealed in a letter from O’Connor, who wrote that after testing negative Tuesday evening, Wednesday morning, Thursday morning, and Friday morning, the president tested positive again late on Saturday morning though antigen testing. “The President has experienced no reemergence of symptoms and continues to feel quite well,” O’Connor wrote. “However, given his positive antigen test, he will reinitiate strict isolation procedures.” RELATED: For more up-to-date information, sign up for our daily newsletter. After testing positive for COVID, Jean-Pierre confirmed that President Biden began taking Paxlovid on July 21. This antiviral medication developed by Pfizer is now a common five-day treatment method for those who test positive for COVID and are at high risk for severe illness—like Biden, who is 79 and therefore more likely to face serious COVID complications. Some people who take Paxlovid, however, have experienced rebound COVID cases that occur between two to eight days after initiation recovery, the Centers for Disease Control and Prevention (CDC) warned in a May 24 health advisory. O’Connor said that “acknowledging the potential for so-called ‘rebound’ COVID positivity” after Paxlovid treatment, Biden was being tested for the virus more regularly to “assure early detection of any return of viral replication.” When he tested positive again on July 30, it was a case of “‘rebound’ positivity,” O’Connor confirmed. The White House physician also revealed that Biden had “unsurprisingly” continued testing positive for COVID the next day, on July 31. Biden is hardly the only person who has tested positive for COVID again following Paxlovid treatment. In June, top White House COVID adviser Anthony Fauci, MD, also experienced a COVID rebound after taking his full five-day treatment, according to The New York Times. The virus expert tested positive again after three days of negative tests—although unlike Biden, Fauci said he did experience a recurrence of symptoms that were worse than during his initial infection. Data from the Department of Health and Human Services indicates that more than 3 million courses of Paxlovid have been administered in the U.S. since Dec. 2021. And Catherine Bennett, PhD, a professor of epidemiology at Deakin University in Australia, told The Washington Post that recent data suggests that rebound cases happen in about 10 percent of Paxlovid recipients. “So not rare, but uncommon,” Bennett said. Nevertheless, most experts have cautioned against worrying too much about Paxlovid rebound cases. White House COVID response coordinator Ashish Jha, MD, told The New York Times that the antiviral medication is still doing a “fantastic job” at its primary goal: keeping people out of the hospital. “We’re not seeing any evidence that rebound leads to people getting super sick and hospitalized,” he told the newspaper.