(Bloomberg) --

President Joe Biden tested negative for Covid-19 for the first time in a week, though he’ll maintain isolation at the White House pending a second negative test, his doctor said.

Biden, 79, “continues to feel very well,” presidential physician Kevin O’Connor said in a letter released by the White House. 

Biden’s “rebound” case, linked by his doctor to the antiviral drug Paxlovid, has stymied the embattled president’s plans to take advantage of a recent Democratic policy wins. He canceled an Aug. 2  trip to Michigan to promote legislation subsidizing US semiconductor manufacturing in the competition with China, though he joined virtually.

The latest antigen test on Biden came back negative on Saturday morning, O’Connor said. “In an abundance of caution, the president will continue his strict isolation measures pending a second negative test as previously described,” the doctor said.

Biden first tested positive on July 21 and ended isolation six days later after twice testing negative on rapid antigen tests. He suffered mild symptoms, including a sore throat, runny nose, fatigue and elevated temperature.

The president tested positive for the second time on July 30 in a type of case seen in some Covid patients who take Pfizer Inc.’s Paxlovid to treat the disease. 

Earlier: Biden’s Covid ‘Rebound’ Case Keeps Him at the White House Again

The US Centers for Disease Control and Prevention guidelines recommend people with rebound cases isolate for five days following a positive test, and if their symptoms are improving and they have no fever, to end isolation but wear a mask for an additional five days with no travel restrictions.

Biden’s case highlighted the issue of rebound cases in a small percentage of people who take Paxlovid, which Biden has touted as a symbol of progress the US has made in controlling the pandemic. 

Rebound cases are typically associated with few or no symptoms, but cause many to resume isolation in accordance with CDC guidelines. Biden had only a mild cough, according to O’Connor.

Pfizer Chief Scientific Officer Mikael Dolsten said the company was working with the Food and Drug Administration to finalize plans for a study of Paxlovid “retreatment” among people who test positive after testing negative.  

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