Casirivimab (REGN10933) is a human monoclonal antibody that targets the SARS-CoV-2 virus, which causes COVID-19. Casirivimab is ineffective against COVID-19 variants. Casirivimab can be used in combination with Imdevimab (HY-P99342), which alters the lung response of K18-hACE2 mice to the SARS-CoV-2 δ variant, effectively reducing viral load and improving symptoms.