President Joe Biden tested positive for Covid-19 again Saturday morning, per a letter from presidential physician Dr. Kevin O’Connor, in what is likely a “rebound” Covid-19 positivity that the doctor noted is “observed in a small percentage of patients treated with Paxlovid.”

Biden has experienced “no reemergence of symptoms, and continues to feel quite well” and will, as a result, not resume treatment, the White House said. O’Connor said the President tested negative on Tuesday evening, Wednesday morning, Thursday morning and Friday morning before testing positive on Saturday morning.

“However, given his positive antigen test, he will reinitiate strict isolation procedures,” the doctor noted. Biden ceased isolating on Wednesday after testing negative on successive antigen tests, celebrating his return in remarks from the White House Rose Garden.