Pfizer's Phase 3 trial of Paxlovid has been found to be very effective in reducing the risk of hospitalization or death. When Paxlovid was given within 3 days of symptom onset the risk was reduced by 89% and 88% when given within 5 days compared to placebo.

This trial data was from an analysis of 2,246 adults.  These results were consistent with the interim analysis announced during November 2021.

This oral drug was given to the eligible participants every 12 hours for 5 days. 

Additionally, an approximately 10-fold decrease in viral load at day 5, relative to placebo, was observed in both EPIC-HR and EPIC-SR, indicating robust activity against SARS-CoV-2 and representing the strongest viral load reduction reported to date for a COVID-19 oral antiviral agent.

The viral load was lower with nirmaltrelvir plus ritonavir than with placebo at day 5 of treatment, with an adjusted mean difference of −0.868 log10 copies per milliliter when treatment was initiated within 3 days after the onset of symptoms. The incidence of adverse events that emerged during the treatment period was similar in the two groups (any adverse event, 22.6% with nirmatrelvir plus ritonavir vs. 23.9% with placebo; serious adverse events, 1.6% vs. 6.6%; and adverse events leading to discontinuation of the drugs or placebo, 2.1% vs. 4.2%). Dysgeusia (5.6% vs. 0.3%) and diarrhea (3.1% vs. 1.6%) occurred more frequently with nirmatrelvir plus ritonavir than with placebo.

Results

Results of this trial were published on February 16, 2022.  The New England Journal of Medicine reported that treatment of symptomatic Covid-19 with nirmatrelvir plus ritonavir resulted in a risk of progression to severe Covid-19 that was 89% lower than the risk with placebo, without evident safety concerns.