The diagnosis comes just days after he recovered from his first case.
President Joe Biden has tested positive for COVID-19 again, just days after he recovered from his previous case of the virus, the White House physician said in a statement Saturday. He is not experiencing any symptoms but will self-isolate again.
In a tweet, the president said he is "still at work" but isolating "for the safety of everyone around me." He will not go on his upcoming trips to Wilmington, Delaware, or Michigan, the White House said.
The president, who is vaccinated and double boosted, feels "quite well" and his physician, Col. Kevin O'Connor, said he will not begin any sort of treatment at this time.
Mr. Biden is experiencing what O'Connor called "'rebound' positivity," which can happen to a small percentage of patients who are treated with the drug Paxlovid.
Mr. Biden was first diagnosed with COVID less than two weeks ago. The president, who is 79 years old, entered isolation and started taking Paxlovid, an antiviral treatment made by Pfizer, White House press secretary Karine Jean-Pierre said in a statement announcing his diagnosis. He experienced only mild symptoms.
After five days, Mr. Biden tested negative Tuesday evening, and ended his isolation period. He subsequently tested negative on Wednesday, Thursday and Friday, his doctor said. However, an antigen test came back positive Saturday morning.
His positive test nine days ago was the first known time Mr. Biden has contracted the coronavirus.
"If you take Paxlovid, you might get symptoms again," CDC director Dr. Rochelle Walensky told CBS News. "We haven't yet seen anybody who has returned with symptoms needing to go to the hospital. So, generally, a milder course."
After a patient recovers, a rebound has been reported to occur two to eight days later. Still, the CDC says the benefits of taking Paxlovid far outweigh the risks. Among unvaccinated people at high risk for severe disease, it reduced the risk of hospitalization and death by nearly 90%, according to the CDC.
At the time, Pfizer said it was seeing a rebound rate of about 2%, but was continuing to monitor patients.
White House COVID-19 coordinator Dr. Ashish Jha told reporters on Monday that data "suggests that between 5 and 8% of people have rebound" after Paxlovid treatment.
Kathryn Watson and Jon LaPook contributed reporting.
This story was originally published by CBS News on July 30, 2022.