Pfizer's oral antiviral Paxlovid significantly cuts risk of severe COVID-19

Only a few days after the UK approved the use of the first oral antiviral to treat COVID-19, Merck’s Lagevrio, Pfizer has ceased enrolment in its phase 2/3 EPIC-HR study of antiviral therapy Paxlovid due to 'overwhelming efficacy'.

Paxlovid is a combination of experimental antiviral PF-07321332 and antiretroviral ritonavir. An interim analysis of the trial data showed that the drug reduced the risk of hospitalisation or death by 89% compared to placebo in non-hospitalised high-risk adults with COVID-19.

The primary endpoint of the EPIC-HR (Evaluation of Protease Inhibition for COVID-19 in High-Risk Patients) study was for people who were treated within three days of symptom onset, but similar results were seen in those treated within five days of symptom onset.

Pfizer has announced that it will submit the data to the Food and Drug Administration (FDA) as part of its ongoing rolling submission as soon as possible.

A protease inhibitor, PF-07321332 is designed to block replication of SARS-CoV-2 while co-administration of the antiretroviral ritonavir – best known as an HIV treatment in HAART (highly active antiretroviral therapy) – slows the breakdown of PF-07321332, increasing its duration of action.

Calling the combination therapy “a real game changer”, Pfizer chairman and CEO Albert Bourla said: “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.”

In its announcement, Pfizer highlighted that, if approved, Paxlovid would be the first oral antiviral that was specifically designed to target SARS-CoV-2. Merck’s Lagevrio (molnupiravir) -3CL protease inhibitor, approved in the UK last week, was originally developed to treat influenza.

The therapy also shows 'potent antiviral in vitro activity' against variants of concern, said Pfizer.

Pfizer is in active discussions with 90 countries over supply contracts for the drug and President Biden has said the US government had already secured millions of doses of the therapy.

Pfizer has committed to 'equitable access' at an affordable price through a tiered pricing approach based on the income level of each country. The company has also 'begun and will continue' to invest up to approximately $1bn to support the manufacturing and distribution of the drug.