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(The Hill) – First lady Jill Biden has tested positive for COVID-19 days after receiving a negative test in a “rebound” case of the virus.

The first lady tested negative on Tuesday before receiving the positive test result on an antigen test on Wednesday afternoon, her office said.

“The First Lady has experienced no reemergence of symptoms, and will remain in Delaware where she has reinitiated isolation procedures,” Kelsey Donohue, the deputy communications director for the first lady, said in a statement.

Biden first tested positive for COVID-19 eight days ago and was given the antiviral drug Paxlovid. She tested positive while on vacation with President Biden and their family in South Carolina. The first lady had mild symptoms and remained there until receiving a negative test, then joined the president in Delaware where he had continued his vacation.

Rebound cases can happen in patients who take Paxlovid when a patient tests negative for the virus, only to test positive again a few days later.

The president had a similar rebound case after taking Paxlovid for his own COVID-19 infection late last month. He remained in isolation for another week because of the rebound case.