Pfizer Pill Reduces Severe COVID-19 Risks by 89% in Phase II/III Study

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Pfizer’s investigational oral antiviral COVID-19 candidate reduced COVID-19-related hospitalization or death by 89% in patients who received it within three days of symptom onset.

Pfizer announced on Nov. 5, 2021, that its investigational novel oral antiviral candidate Paxlovid (PF-07321332; ritonavir) significantly reduced severe risks of COVID-19 in a recent clinical trial. According to an interim analysis of the Phase II/III Evaluation of Protease Inhibition for COVID-19 in High-Risk Patients (EPIC-HR) trial, ritonavir demonstrated an 89% reduction in risk of COVID-19-related hospitalization or death from any cause within three days of onset relative to the placebo group.

EPIC-HR was a randomized, double-blind study of non-hospitalized patients with COVID-19 considered to be at high risk of progressing to severe illness. Enrolled individuals had a laboratory-confirmed diagnosis of SARS-CoV-2 infection within a five-day period with mild to moderate symptoms. They were required to have at least one characteristic or underlying medical condition associated with an increased risk of developing severe illness from COVID-19.

Two groups of patients (randomized 1:1 to receive ritonavir or placebo every 12 hours for five days) were evaluated: those treated within three days of symptom onset, and those treated within five days. In the former group, 0.8% of patients who received ritonavir (3/389) were hospitalized through Day 28; no deaths were reported in this patient group. In that same time frame, 7.0% of patients who received placebo (27/385) were hospitalized; seven deaths were reported in this group.

These values were comparable to those in the five-day group, which reported 1.0% (6/607) and 6.7% (41/612) hospitalization rates, respectively. No deaths were reported in this ritonavir group, while three patients in the placebo group died.

Treatment-emergent adverse events were comparable between ritonavir (19%) and placebo (21%). Among the patients evaluable for treatment-emergent adverse events, fewer serious adverse events (1.7% vs. 6.6%) and discontinuation of study drug due to adverse events (2.1% vs. 4.1%) were observed in patients dosed with ritonavir compared to placebo.


“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, in a company press release. “Given the continued global impact of COVID-19, we have remained laser-focused on the science and fulfilling our responsibility to help healthcare systems and institutions around the world while ensuring equitable and broad access to people everywhere.”

According to the press release, at the recommendation of an independent data monitoring committee and FDA, Pfizer will cease further enrollment in the study. Pfizer plans to submit the data as part of its ongoing rolling submission to FDA for Emergency Use Authorization as soon as possible.

Source: Pfizer