US First Lady Jill Biden has tested positive for COVID-19, the White House has said.
The 71-year-old had tested negative on Monday during a regular testing session, but developed cold-like symptoms that evening.
She tested negative on a rapid antigen test before a PCR test came back positive.
Spokesperson Elizabeth Alexander said the first lady has had two vaccinations and two booster jabs against the disease.
She is experiencing mild symptoms and has also been prescribed the antiviral drug Paxlovid.
Mrs Biden and her husband US President Joe Biden are on holiday in the US state of South Carolina.
She will isolate there for at least five days, the White House said, and will return home after two consecutive negative tests.
Mr Biden caught the virus last month but experienced a rebound case on 7 August.
The president was also given Paxlovid.
The drug can reduce hospitalisation and death among patients by 90% if administered within five days of symptoms appearing.
But it is also associated with a higher incidence of rebound infections, where patients test positive again days after the drug has helped them clear the initial infection.
Mr Biden tested negative on Tuesday, the White House said, but will wear a face mask indoors for 10 days, in line with guidance from the Centers for Disease Control and Prevention.
He has returned to work.