U.S. President Joe Biden again tested positive for COVID-19 on Sunday, but continues to feel well, his personal physician reported.

Biden, who tested positive Saturday after recovering from a first bout of the coronavirus last week, is continuing to isolate at the residence in the White House after the new diagnosis, Dr. Kevin O’Connor said in a memo.

O’Connor said the 79-year-old chief executive is “very specifically conscientious to protect” White House staff, Secret Service security agents and others who need to be in relatively close contact to him.

After testing negative for the coronavirus for several days, Biden tested positive, which O’Connor attributed to a “rebound” in a “small percentage of a patients” who had been prescribed the drug Paxlovid to treat their initial coronavirus diagnosis.