WASHINGTON (WTVO) —President Joe Biden tested positive for COVID-19 again Saturday morning.

Presidential physician Dr. Kevin O’Connor described it as a “rebound” COVID-19 positivity in a letter, according to CNN. The doctor noted that it is “observed in a small percentage of patients treated with Paxlovid.”

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

“However, given his positive antigen test, he will reinitiate strict isolation procedures,” O’Connor said.

While the president is not experiencing any symptoms and stopped isolating on Wednesday, he will resuming isolation after the positive test.