First lady Jill Biden tests positive for 'rebound' COVID-19 case

First lady Jill Biden has tested positive for COVID-19 again in what the White House is calling a "rebound" case.

"After testing negative on Tuesday, just now, the First Lady has tested positive for COVID-19 by antigen testing. This represents a 'rebound' positivity," the first lady's deputy communications director Kelsey Donohue said in a statement.

"The First Lady has experienced no reemergence of symptoms, and will remain in Delaware where she has reinstated isolation procedures. The White House Medical Unit has conducted contact tracing and close contacts have been notified," Donohue added.

Biden first tested positive for COVID on August 15 while on vacation in Kiawah Island, South Carolina. She was reported to have "mild symptoms" at the time and began isolating until she received two consecutive negative COVID-19 tests. Biden was prescribed the antiviral drug Paxlovid to treat her symptoms and had her second consecutive negative test on Sunday, when she traveled from South Carolina to meet President Joe Biden in Delaware.

Both Jill Biden and her husband the president have been fully vaccinated and twice-boosted with the Pfizer-BioNTech mRNA vaccine.

President Biden tested negative Wednesday, according to CNN. An official said Biden will wear a face mask for 10 days in accordance with U.S. Centers for Disease Control and Prevention protocol.

The president was also treated for COVID-19 last month, and he later tested positive with a rebound case following several initial negative case.

Donohue said Jill Biden will isolate at the family beach house in Delaware until she has recovered and tested negative.

The CDC says that a brief return of COVID-19 symptoms may occur in some patients independent of treatment with Paxlovid and regardless of vaccination status. People who come down with rebound cases after taking Paxlovid are reported to experience mild symptoms; none have had severe disease, the CDC says.

People who experience a rebound infection are recommended to isolate for five days. After that period, an individual who is fever-free for 24 hours without using fever-reducing medications may exit isolation but is recommended to wear a mask for 10 more days.

In June, White House chief medical adviser Dr. Anthony Fauci also experienced a rebound infection after taking Paxlovid.

Paxlovid is a COVID-19 pill manufactured by Pfizer that has received emergency use authorization from the U.S. Food and Drug Administration to treat people at high risk of severe disease. The drug showed an 89% reduction in risk of hospitalization and death among COVID-19 patients in clinical trials and has been described as a "game changer" for the pandemic.