Real-world Effectiveness of Casirivimab and Imdevimab in Patients With COVID-19 in the Ambulatory Setting: An Analysis of Two Large US National Claims Databases

Background: In a phase III clinical trial, casirivimab and imdevimab (CAS+IMD) reduced the composite risk of COVID-19-related hospitalizations or all-cause mortality in outpatients at risk of severe disease. This study assessed the real-world effectiveness of CAS+IMD. Methods: Data from Optum Clinformatics Data Mart (CDM) and IQVIA Pharmetrics Plus (PMTX+) were used to identify patients diagnosed with COVID-19 in ambulatory settings between December 2020 and March 2021 (PMTX+) and June 2021 (CDM), and either treated with CAS+IMD or untreated but treatment-eligible under Emergency Use Authorization. CAS+IMD-treated patients were matched to untreated patients and followed up to 30 days for the composite of all-cause mortality or COVID-19-related hospitalizations (CDM) and COVID-19-related hospitalizations (PMTX+). Kaplan-Meier estimators were used to calculate outcome risks; Cox proportional-hazard models provided adjusted hazard ratios (aHR) with 95% confidence intervals (CI). Results: For CDM, 1116 CAS+IMD-treated patients were matched to 5294 untreated patients; for PMTX+, 3280 CAS+IMD-treated patients were matched to 16 284 untreated patients. The 30-day composite risk was 2.1% and 5.3% in the treated and untreated cohorts, respectively (CDM), and the 30-day risk of COVID-19-related hospitalization was 1.9% and 4.8%, respectively (PMTX+), translating to a 61% lower risk of hospitalization or mortality with CAS+IMD: CDM aHR 0.39 (95% CI 0.26-0.60), PMTX+ aHR 0.39 (95% CI 0.30-0.51). The benefit of treatment was maintained across subgroups, and earlier intervention was associated with improved outcomes. Conclusions: Results of this real-world study further support randomized clinical trial findings that treatment with CAS+IMD reduces the risk of hospitalization and mortality.