Effectiveness of Casirivimab and Imdevimab Antibody Combination in Immunocompromised Hospitalized Patients With Coronavirus Disease 2019: A Post Hoc Analysis in a Phase 1/2/3 Double–Blind Trial

BACKGROUND: Individuals who are immunocompromised (IC) are at high risk for severe coronavirus disease 2019 (COVID-19). METHODS: Post hoc analyses of a double-blind trial conducted prior to Omicron (June 2020–April 2021), in hospitalized patients with COVID-19 assessed viral load, clinical outcomes, and safety of casirivimab plus imdevimab (CAS + IMD) versus placebo in IC versus overall study patients. RESULTS: Ninety-nine of 1940 (5.1%) patients were IC. IC versus overall patients were more frequently seronegative for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies (68.7% vs 41.2%) and had higher median baseline viral loads (7.21 vs 6.32 log(10) copies/mL). On placebo, IC versus overall patients had slower viral load declines. CAS + IMD reduced viral load in IC and overall patients; least-squares mean difference versus placebo in time-weighted average change from baseline viral load at day 7 was −0.69 (95% confidence interval [CI], −1.25 to −.14) log(10) copies/mL for IC patients and −0.31 (95% CI, −.42 to −.20) log(10) copies/mL for overall patients. For IC patients, the cumulative incidence of death or mechanical ventilation at day 29 was lower with CAS + IMD (11.0%) versus placebo (17.2%), consistent with overall patients (15.7% CAS + IMD vs 18.3% placebo). IC and overall patients receiving CAS + IMD exhibited similar rates of treatment-emergent adverse events (30.4% and 26.6%, respectively), grade ≥2 hypersensitivity or infusion-related reactions (1.4% and 2.5%), and deaths (8.7% and 12.2%). CONCLUSIONS: IC patients were more likely to exhibit high viral loads and be seronegative at baseline. For susceptible SARS-CoV-2 variants, CAS + IMD reduced viral load and resulted in fewer death or mechanical ventilation events in IC and overall study patients. There were no new safety findings among IC patients. Clinical Trials Registration. NCT04426695.