Efficacy of Antibodies and Antiviral Drugs against Covid-19 Omicron Variant

e Efficacy of Antibodies and Antiviral Drugs against Covid-19 Omicron VariantTo the Editor: In November 2021, the B.1.1.529(omicron) variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was detected in South Africa. 1 Since then, omicron has rapidly spread around the world.On November 26, 2021, the World Health Organization designated omicron as a variant of concern.The omicron variant was found to have at least 33 mutations (29 amino acid substitutions, 1 insertion of three amino acids, and 3 small deletions) in its spike (S) protein, as compared with early SARS-CoV-2 strains identified in Wuhan, China. 2 Notably, 15 of the 29 substitutions were in the receptorbinding domain of the S protein, which is the primary target for monoclonal antibody-based therapy.This finding suggests that the monoclonal antibodies that have been approved by the Food and Drug Administration (FDA) may be less effective against the omicron variant.Accordingly, we examined the neutralizing ability of FDA-approved and investigational therapeutic monoclonal antibodies (individually and in combination) against omicron and other variants of concern.Using a live-virus focus reduction neutralization assay (FRNT), we assessed the neutralizing activities of monoclonal antibodies against hCoV-19/Japan/NC928-2N/2021 (omicron; NC928), which was isolated from a traveler who arrived in Japan from Namibia; SARS-CoV-2/UT-NC002-1T/Human/2020/Tokyo (NC002), an early SARS-CoV-2 strain from February 2020; SARS-CoV-2/UT-HP127-1Nf/Human/2021/Tokyo (alpha; HP127); hCoV-19/USA/MD-HP01542/2021 (beta; HP01542); hCoV-19/Japan/TY7-503/2021 (gamma; TY7-503); and hCoV-19/USA/WI-UW-5250/ 2021 (delta; UW5250).Whole-genome sequencing analysis of the NC928 omicron virus stock revealed that the variant had the 15 substitutions