Move over molnupiravir, here comes Pfizer’s Paxlovid for Covid

A good week for Pfizer’s Covid-19 efforts has ended with topline data on its antiviral that could not look much better. Paxlovid, as PF-07321332 is now called, generated an 89% reduction in the risk of hospitalisation or death versus placebo in patients at high risk of severe disease who were treated at home. The results are from an interim analysis of the now-halted phase 2/3 Epic-HR trial. That risk reduction figure is derived from patients treated within three days of symptom onset, the study’s primary endpoint. Only three of 389 Paxlovid-treated subjects were hospitalised, versus 27 of 385 in the placebo arm, generating a highly statistically difference (p<0.0001). Similarly impressive reductions were seen in patients treated at five days and, in what will surely mean a swift emergency use authorisation, no deaths were reported in the Paxlovid arm through day 28, against 10 in the placebo group. Comparing across trials is never ideal, though the result seems easily to beat the 50% reduction generated by Merck & Co and Ridgeback’s molnupiravir in the similar Move-Out trial. Little wonder that Pfizer opened 10% higher today, while Merck shares dropped a similar amount.

Paxlovid's late-stage clinical programme 
Trial Setting  Results
Epic-HR Non-hospitalised adults at high risk of severe illness Initiated in Jul 2021; 89% risk reduction vs placebo at interim analysis at 70% enrolment; almost half of subjects US-based
Epic-SR  Non-hospitalised adults at low risk of severe illness Data due Q1 2022
Epic-PEP Post-exposure prophylaxis, adults with household contacts Data due Q1/Q2 2022
Note: Paxlovid is a co-administration of PF-07321332 with low dose ritonavir; the latter helps slow the metabolism of the former. Source: company statements.

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