Pfizer Inc. (NYSE: PFE) today shared results from multiple studies demonstrating that the in vitro efficacy of nirmatrelvir, the active main protease (Mpro) inhibitor of PAXLOVID™ (nirmatrelvir [PF-07321332] tablets and ritonavir tablets), is maintained against the SARS-CoV-2 variant Omicron. Taken together, these in vitro studies suggest that PAXLOVID has the potential to maintain plasma concentrations many-fold times higher than the amount required to prevent Omicron from replicating in cells.