Pfizer reports new study results about oral antiviral treatment for COVID-19

Dec. 15, 2021

Pfizer has released final results from a Phase 2/3 trial of PAXLOVID, showing that the COVID-19 oral antiviral medication significantly reduced the risk of hospitalization or death for any cause by 89%, compared to placebo, in non-hospitalized, high-risk adult patients with COVID-19 treated within three days of symptom onset.

These results, which involved the analysis of data from all 2,246 adults enrolled in the study, were consistent with the interim analysis announced in November 2021.

Pfizer said the data about the treatment, which consists of nirmatrelvir combined with ritonavir, have been shared with the U.S. Food and Drug Administration (FDA) as part of an ongoing rolling submission for emergency use authorization (EUA). The New York Times reported that the agency may decide whether to authorize the medication within a few days.

A total of 0.7% of patients who received PAXLOVID were hospitalized through day 28 following randomization (5/697 hospitalized with no deaths), compared to 6.5% of patients who received placebo and were hospitalized or died (44/682 hospitalized with 9 subsequent deaths).

The relative risk reduction was 94% in patients 65 years of age or older, one of the populations at highest risk for hospitalization or death. In the overall study population through Day 28, no deaths were reported in patients who received PAXLOVID as compared to 12 (1.2%) deaths in patients who received placebo.

In a secondary endpoint, SARS-CoV-2 viral load at baseline and Day 5 have been evaluated for 499 patients. After accounting for baseline viral load, geographic region, and serology status, PAXLOVID reduced viral load by approximately 10-fold, relative to placebo. Pfizer said this indicates “robust activity against SARS-CoV-2 and representing the strongest viral load reduction reported to date for an oral COVID-19 agent.”

Another secondary endpoint showed a 70% reduction in hospitalization and no deaths in the treated population for any cause compared to placebo.

PAXLOVID is an investigational SARS-CoV-2 protease inhibitor antiviral therapy. It was developed to be administered orally so that, if authorized or approved, it can be prescribed at the first sign of infection or at first awareness of exposure. Nirmatrelvir, which originated in Pfizer laboratories, is designed to block the activity of the SARS-CoV-2-3CL protease, an enzyme that the coronavirus needs to replicate. Co-administration with a low dose of ritonavir helps slow the metabolism, or breakdown, of nirmatrelvir, so it can remain active in the body for longer periods of time at higher concentrations.

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