Final results from the phase 2/3 EPIC-HR study evaluating the investigational COVID-19 oral antiviral candidate Paxlovid™ (PF-07321332/ritonavir) showed a significant reduction in the risk of hospitalization or death in nonhospitalized symptomatic adults with COVID-19 who were at an increased risk of progressing to severe illness.

Paxlovid consists of PF-07321332, which inhibits the viral replication of SARS-CoV-2 by blocking the activity of the SARS-CoV-2-3CL protease, and low-dose ritonavir. Coadministration with low-dose ritonavir slows the metabolism of PF-07321332 and prolongs its activity.

The randomized, double-blind, 2-arm, EPIC-HR study ( Identifier: NCT04960202) included 2246 patients with laboratory-confirmed SARS-CoV-2 infection and 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.

Final results were consistent with the interim analysis announced in November 2021 demonstrating that Paxlovid significantly reduced the risk of COVID-19-related hospitalization or death from any cause by 89% (within 3 days of symptom onset) compared with placebo (P <.0001). Through day 28, 0.7% (5/697) of patients in the Paxlovid arm were hospitalized compared with 6.5% (44/682) of those in the placebo arm.

Paxlovid also reduced the risk of hospitalization or death from any cause by 88% in patients treated within 5 days of symptom onset (secondary endpoint) compared with placebo (P <.0001). Through day 28, 0.8% (8/1039) of patients in the Paxlovid arm were hospitalized vs 6.3% (66/1046) of those in the placebo arm.

Among patients 65 years of age and older, 1.1% (1/94) of patients treated with Paxlovid were hospitalized compared with 16.3% (16/98) of those in the placebo arm (P <.0001).

In the overall study population, there were no deaths reported in the Paxlovid arm and 12 deaths in the placebo arm.

“This news provides further corroboration that our oral antiviral candidate, if authorized or approved, could have a meaningful impact on the lives of many, as the data further support the efficacy of Paxlovid in reducing hospitalization and death and show a substantial decrease in viral load,” said Albert Bourla, Chairman and CEO, Pfizer. 

In November 2021, the Company submitted a request for Emergency Use Authorization to the Food and Drug Administration (FDA) for Paxlovid.


Pfizer announces additional phase 2/3 study results confirming robust efficacy of novel COVID-19 oral antiviral treatment candidate in reducing risk of hospitalization or death. News release. Pfizer Inc. Accessed December 14, 2021.