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Pfizer anti-viral

November 10, 2021

Pfizer, similar to Merck, has announced the efficacy of their anti-viral drug called PAXLOVID against SARS-CoV-2.  The reported 89% efficacy against serious disease and 100% efficacy against death and they are making headlines. Pfizer’s anti-viral drug is different than the one from Merck in that it is not just a repurposed drug like the Merck product but rather the first drug designed to specifically target SARS-CoV-2 and the first to date to progress this far in human clinical trials.

The trial’s focus was on unvaccinated patients at a high-risk of developing severe COVID-19. The primary cohort were administered a five-day course of the antiviral pill, starting within three days of symptoms appearing. Their results from a scheduled interim analysis showed that out of 389 participants taking the antiviral, only three hospitalizations were reported, with no deaths. This was compared to 385 participants in a placebo group, who had 27 hospitalizations and seven deaths.

Comparing the risk ratios of hospitalizations and deaths, they showed that the antiviral is 89 percent at reducing risk and, therefore, effective at preventing hospitalization or death. Pfizer reported the results to be highly statistically significant (p<0.0001). Although they did not report or name a single statistical test for these results in their press releases, we can only infer once again their use of relative risks calculated from potentially a Poisson regression, however, we can only infer. Given that they reported the results at an interim analysis, we also have no idea at which alpha level of significance they were testing and how stringent the criterion was.  Perhaps when they publish these results more formally we will better understand the statistical methods used behind obtaining these results. Thereafter, Pfizer has decided to stop enrollment into the trial after review by their DSMB and consultation with the FDA.

Written by,

Usha Govindarajulu



COVID-19, anti-viral, clinical trial, relative risks, biostatistics, Usha Govindarajulu




Haridy, Rich (November 7, 2021) “Pfizer’s COVID-19 pill cuts hospitalization or death by nearly 90%”

Pfizer (November 5, 2021) “Pfizer’s Novel COVID-19 Oral Antiviral Treatment Candidate Reduced Risk Of Hospitalization Or Death By 89% In Interim Analysis Of Phase 2/3 EPIC-HR Study”×575.jpg?w=1155&h=1528