Paxlovid, once hailed as a "game-changer" for its ability to treat COVID-19 infections at home, is becoming one of the pandemic's biggest enigmas.
The intrigue: There's growing concern about the link between Pfizer's antiviral pill and COVID rebound, in which patients test positive or have symptoms days after a course of the drug is completed. President Biden, First Lady Jill Biden and NIAID Director Anthony Fauci have each relapsed.