Effectiveness of Casirivimab-Imdevimab Monoclonal Antibody Treatment Among High-Risk Patients With Severe Acute Respiratory Syndrome Coronavirus 2 B.1.617.2 (Delta Variant) Infection

SUMMARY: Retrospective analysis of the post–propensity score (PS)–matched cohort of 8426 outpatients balanced in clinical and demographic covariates showed that treatment with casirivimab-imdevimab monoclonal antibody was effective against the SARS-CoV-2 Delta variant to reduce hospitalization, mortality, and intensive care unit admission rates within 30 days. BACKGROUND: Real-world data on the effectiveness of neutralizing casirivimab-imdevimab monoclonal antibody (Cas-Imd mAb) against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection among high-risk patients may inform the response to future SARS-CoV-2 variants. METHODS: This study covers an observational retrospective data analysis in Banner Health Care System sites, mainly in Arizona. During the study period, the prevalence of SARS-CoV-2 Delta variant was between 95% and 100%. Of 29 635 patients who tested positive for coronavirus disease 2019 (COVID-19) between 1 August 2021 and 30 October 2021, in the Banner Health Care System, the study cohort was split into 4213 adult patients who received Cas-Imd mAb (1200 mg) treatment compared to a PS-matched 4213 untreated patients. The primary outcomes were the incidence of all-cause hospitalization, intensive care unit (ICU) admission, and mortality within 30 days of Cas-Imd mAb administration or Delta variant infection. RESULTS: Compared to the PS-matched untreated cohort, the Cas-Imd mAb cohort had significantly lower all-cause hospitalization (4.2% vs 17.6%; difference in percentages, −13.4 [95% confidence interval {CI}, −14.7 to −12.0]; P < .001), ICU admission (0.3% vs 2.8%; difference, −2.4 [95% CI, −3.0 to −1.9]; P < .001), and mortality (0.2% vs 2.0%; difference, −1.8 [95% CI, −2.3 to −1.3]; P < .001) within 30 days. The Cas-Imd mAb treatment was associated with lower rate of hospitalization (hazard ratio [HR], 0.22 [95% CI, .19–.26]; P < .001) and mortality (HR, 0.11 [95% CI, .06–.21]; P < .001). CONCLUSIONS: Cas-Imd mAb treatment was associated with a lower hospitalization rate, ICU admission, and mortality within 30 days among patients infected with the SARS-CoV-2 Delta variant.