It’s a step forward and a step back at Pfizer Inc. Even as Pfizer and its partner Biontech SE finished filing an emergency use authorization application with the U.S. FDA seeking to field an updated booster dose of their omicron COVID vaccine, the regulator has made a request of its own, for more data on the company's oral antiviral, Paxlovid (nirmatrelvir + ritonavir), for treating COVID-19. An Aug. 5, 2022, letter from the FDA stipulates post-EUA requirements for Paxlovid, including that Pfizer conduct a trial in patients with a relapse of COVID symptoms, longhand for a “rebound,” after an initial Paxlovid treatment course.