Pfizer's COVID-19 antiviral is expected to work against the omicron variant

Pfizer expects its antiviral pill Paxlovid to provide protection against the omicron variant of the coronavirus, which has caused concern around the world that existing medications and vaccines would not work against the newly mutated virus.

Omicron's emergence spurred fears that the pandemic was entering a new phase. But Pfizer now says that its antiviral pill, which previously recorded robust data showing it could prevent hospitalization and death, should be able to maintain antiviral activity against the variant.

New York-based Pfizer presented a final analysis from a phase 2/3 study called Epic-HR, which showed that Paxlovid reduced the risk of hospitalization or death in high-risk adult patients by 89% within three days of onset compared to placebo. The final analysis confirmed the earlier results. These data have been submitted to the FDA as part of a rolling submission for an emergency use authorization.

The omicron analysis was based on in vitro data, which means the studies were performed in a lab rather than in a human body. Pfizer said Paxlovid, also known as nirmatrelvir, previously showed antiviral activity against other variants of concern, including delta, which has caused its own wave of infections in the U.S. the past few months.

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“Emerging variants of concern, like omicron, have exacerbated the need for accessible treatment options for those who contract the virus, and we are confident that, if authorized or approved, this potential treatment could be a critical tool to help quell the pandemic,” Pfizer CEO Albert Bourla said in a statement.

The main concern about the variant has been that it can be resistant to treatments that work on the spike protein of the coronavirus, which is how the virus invades human cells. But Pfizer says its pill works intracellularly to inhibit viral replication, so the spike protein mutations are not a concern.

With the final results shoring up Paxlovid’s potential in high-risk patients, Pfizer also reported that interim results from lower-risk patients did not appear to be as strong. An interim analysis of a different ongoing study called Epic-SR with standard-risk adults did not meet its primary endpoint. That goal was the self-reported, sustained alleviation of all symptoms for four straight days. Paxlovid did, however, reduce hospitalizations by 70% and no deaths were recorded, which was a secondary goal of the trial.

In both studies, Paxlovid showed a tenfold decrease in viral load at day five when compared to placebo. This suggests Paxlovid spurs robust antiviral activity against the coronavirus, which Pfizer said is the strongest recorded yet for an oral antiviral agent.

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That statement is, of course, a direct shot across the bow to Merck, which originally posted strong data for its candidate, called molnupiravir, back in October. That data suggested the Merck drug could halve the risk of hospitalization and prevent deaths. But a final analysis of the late-stage study—quietly released over Thanksgiving last month—showed a sharp decline in efficacy, down to just 30%.

Paxlovid will be administered twice daily for five days along with ritonavir, which helps slow down the metabolism of the antiviral.

It’s already been a busy week for Pfizer, which announced a $6.7 billion acquisition of Arena Pharmaceuticals on Monday. The acquisition will help bulk up the pharma giant’s pipeline in the latter half of the decade when the wave of cash from the new COVID franchise—both Paxlovid and the vaccine Comirnaty—is expected to crest.