Dr. Rochelle Walensky, U.S. Centers for Disease Control and Prevention Director, testifies during a Senate Health, Education, Labor, and Pensions Committee hearing on the monkeypox outbreak, in Capitol Hill in Washington, U.S., September 14, 2022.

Walensky again tested positive for COVID with mild symptoms on Oct. 31 after completing a course of Pfizer's Paxlovid, having contracted the infection on Oct. 22

Walensky is the third senior government executive, after U.S. President Joe Biden and National Institute of Allergy and Infectious Diseases Director Dr Anthony Fauci to experience recurrent viral infection following the first course of Paxlovid.

Some people who took the antiviral drug have suffered from a relapse or a rebound soon after the five-day treatment course, studies have shown.