US first lady Jill Biden on Wednesday tested positive for Covid-19 in a case of “rebound” positivity, the White House said in a statement.
She is not experiencing any symptoms but she will re-enter isolation in Delaware, where she is currently located.
“After testing negative on Tuesday, just now, the first lady has tested positive for Covid-19 by antigen testing,” her deputy communications director Kelsey Donohue said.
The White House confirmed that it is likely to be a “rebound” case experienced after she tested negative following a full course of Pfizer's five-day paxlovid antiviral treatment.
Ms Biden first tested positive two weeks ago at the end of a Biden family holiday on August 16 and remained in South Carolina in isolation. She experienced “cold-like symptoms” and took paxlovid.
After five days of isolation, the first lady tested negative twice on Sunday and left South Carolina to join Mr Biden in Delaware.
The Bidens have both received four doses of Covid-19 vaccine.
The White House said Mr Biden tested negative on Wednesday but as a “close contact” of the first lady's, he will wear a face mask around others or while in indoor spaces for the next 10 days.
The president battled Covid-19 for two weeks in July, during which he also experienced a “rebound” case after taking paxlovid.
The Biden administration says that “rebound” cases are rare, but limited research suggests it is more common than previously thought: a team at Brigham and Women’s Hospital in Boston, Massachusetts, conducted a study that found that more than a quarter of participants experienced “rebound” symptoms after taking paxlovid. The study, however, has not yet been peer reviewed.
Paxlovid is still recommended as an initial treatment since it overwhelmingly helps prevent severe illness, hospital admission and death.
The US Food and Drug Administration (FDA) has not recommended that doctors prescribe it a second time if individuals test positive again.
“There is no evidence of benefit at this time for a longer course of treatment [ …] or repeating a treatment course of paxlovid in patients with recurrent Covid-19 symptoms following completion of a treatment course,” John Farley, the director of the FDA Office of Infectious Diseases, said in an interview in May.
The FDA last week ordered Pfizer to study whether infected people should take longer courses of paxlovid.
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