What was once effective is now a non-starter. Newly updated guidelines from the World Health Organization (WHO) caution against using the COVID-19 treatments sotrovimab, from GSK plc and Vir Biotechnology Inc., and Regen-Cov (casirivimab + imdevimab), from Regeneron Pharmaceuticals Inc. Omicron, the group said, has rendered the monoclonal antibodies ineffective.