Pfizer announced that the interim analysis of its phase 2/3 study evaluating the investigational COVID-19 oral antiviral candidate, Paxlovid (PF-07321332/ritonavir), demonstrated a significant reduction in the risk for hospitalization or death in nonhospitalized symptomatic adults with COVID-19 who were at an increased risk of progressing to severe illness.

Paxlovid is an investigational SARS-CoV-2 protease inhibitor consisting of PF-07321332 and low-dose ritonavir. PF-07321332 inhibits the viral replication of SARS-CoV-2 by blocking the activity of the SARS-CoV-2-3CL protease. The co-administration with low-dose ritonavir slow the metabolism of PF-07321332 to prolong activity.

The randomized, double-blind, 2-arm, EPIC-HR study ( Identifier: NCT04960202) included 1219 patients with laboratory-confirmed diagnosis of SARS-CoV-2 infection within a 5-day period with mild to moderate symptoms. Patients were required to have at least 1 characteristic or underlying medical condition associated with an increased risk of developing severe illness from COVID-19. Patients were randomly assigned 1:1 to receive either Paxlovid or placebo orally every 12 hours for 5 days.

Interim analysis showed that patients in the Paxlovid treatment arm had an 89% reduction in the risk of COVID-19-related hospitalization or death from any cause within 3 days of symptom onset (primary endpoint) compared with placebo (P <.0001). Through Day 28, 0.8% of patients (3/389) in the Paxlovid arm were hospitalized with no deaths compared with 7% (27/385) of those in the placebo arm who were hospitalized with 7 subsequent deaths (P <.0001).

Additionally, there were similar findings observed in patients treated within 5 days of symptom onset with 1% of patients (6/607) in the Paxlovid arm who were hospitalized with no deaths through Day 28 compared with 6.7% (41/612) of those in the placebo arm who were hospitalized with 10 subsequent deaths (P <.0001). In the overall study population, there were no deaths reported in the Paxlovid arm and 10 deaths in the placebo arm.

Pfizer has decided to stop the study based on a recommendation from an independent Data Monitoring Committee and in consultation with the Food and Drug Administration (FDA) due to “overwhelming efficacy.” The Company plans to submit these data as part of an ongoing rolling submission to the FDA for Emergency Use Authorization as soon as possible. 

“Today’s news is a real game-changer in the global efforts to halt the devastation of this pandemic. These data suggest that our oral antiviral candidate, if approved or authorized by regulatory authorities, has the potential to save patients’ lives, reduce the severity of COVID-19 infections, and eliminate up to nine out of ten hospitalizations,” said Albert Bourla, Chairman and CEO, Pfizer.


Pfizer’s novel COVID-19 oral antiviral treatment candidate reduced risk of hospitalization or death by 89% in interim analysis of phase 2/3 EPIC-HR study. News release. Pfizer Inc. Accessed November 5, 2021.