CDC Director Dr. Rochelle Walensky tested positive for COVID-19 again on Sunday, 10 days after initially contracting the virus.
Walensky, who is up to date on her vaccines, started a course of Pfizer's antiviral drug Paxlovid when she first started developing symptoms on Oct. 21.
Her symptoms improved and she tested negative, but she tested positive again in an apparent rebound case on Sunday.
Walensky is the third high-profile government official to experience a rebound COVID-19 case after taking Paxlovid, which was approved in December for patients at risk of severe infection.
President Joe Biden tested positive for COVID-19 in a rebound case in July after testing negative for four days.
Dr. Anthony Fauci, who is stepping down at the end of this year, also suffered a rebound case in June.
Walensky is now isolating at home and working virtually, the CDC said.