President Biden tests positive again for COVID-19 in 'rebound' case

• Paxlovid is an at-home antiviral therapy for those at higher risk for severe illness from COVID-19.
• Some people who have received Paxlovid have gotten rebound COVID-19 infections, including Dr. Anthony Fauci
• Biden has returned to isolation. The CDC advises people with rebound cases isolate for five days.

WASHINGTON — President Joe Biden tested positive again Saturday morning for COVID-19 as part of a virus "rebound" that patients treated with the antiviral medication Paxlovid sometimes experience, his doctor said. 

Biden has no reemergence of symptoms, Kevin O'Connor, physician to the president, said in a letter, and as a result, his doctors will not restart medical treatment. 

Still, Biden said he's returned to isolation.

"Folks, today I tested positive for COVID again," Biden said in a statement on Twitter. "This happens with a small minority of folks. I’ve got no symptoms but I am going to isolate for the safety of everyone around me. I’m still at work, and will be back on the road soon."

More:'I'm feeling great': President Biden tests negative for COVID-19, ends isolation

Paxlovid is an at-home antiviral therapy for those at higher risk for severe illness from COVID-19. Biden, 79, was at risk because of his age. He has been vaccinated and boosted against the virus.

The Centers for Disease Control and Prevention advises that people who test positive for COVID-19 again after taking the drug Paxlovid should isolate for another five days.

Biden will remain isolated until he tests negative, the White House said. The president canceled trips he planned to take Sunday to his home in Wilmington, Del. and Tuesday to Hemlock, Mich., where he was scheduled to deliver remarks on the recently approved CHIPS and Science bill, which aims to reduce U.S. reliance on Chinese computer chips by boosting U.S. manufacturing.

Biden made his first public appearance Wednesday after testing positive for COVID-19 for the first time July 21. The president tested negative Tuesday night and Wednesday morning, prompting him to end isolation, and again on Thursday and Friday mornings, according to O'Connor.

Biden gave remarks in the Rose Garden at the White House Wednesday, crediting vaccinations and Paxlovid for a speedy recovery. “I’m feeling great,” Biden said. “I got through it with no fear.”

Some people who have received Paxlovid have gotten rebound COVID-19 infections, which can happen as soon as a few days after testing negative. 

In the small share of Paxlovid patients whose infections come back, they don't get sick enough to require hospitalization, White House COVID-19 response coordinator Dr. Ashish Jha has said. 

It's not clear whether a rebound after taking the antiviral Paxlovid is any different than a rebound without the drug. In the trial that led to Paxlovid's authorization, 2% of those who took the medication and nearly the same percentage of those who didn't experienced rebounds.

There's little data yet on whether someone experiencing a COVID-19 rebound produces enough live virus to infect those around them. 

During Biden's first isolation, the White House sought to portray a president still working, releasing photos of him on the phone and at his desk, featuring Biden in prerecorded videos and scheduling virtual events.

More:Dr. Anthony Fauci tests positive for COVID-19, is experiencing mild symptoms

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and Biden's chief medical adviser, also experienced a rebound of his COVID-19 infection in June that he said was the result of Paxlovid.

Fauci told CNN that he felt worse the second time with COVID-19 than the first.

"Over the next day or so I started to feel really poorly, much worse than in the first go around," he said.

Contributing: Karen Weintraub 

Reach Joey Garrison on Twitter @joeygarrison.