Effectiveness of Subcutaneous Casirivimab and Imdevimab in Ambulatory Patients with COVID-19

Introduction: Data on real-world effectiveness of subcutaneous (SC) casirivimab and imdevimab (CAS+IMD) for the treatment of coronavirus disease 2019 (COVID-19) are limited. The objective of this study was to assess the effectiveness of SC CAS+IMD versus no antibody treatment among patients with COVID-19.

Methods: This retrospective cohort study linked Komodo Health and CDR Maguire Health and Medical data. Patients diagnosed with COVID-19 in ambulatory settings (August 1-October 30, 2021) treated with SC CAS+IMD were exact- and propensity score-matched to fewer than five untreated treatment-eligible patients and followed for the composite endpoint of 30-day all-cause mortality or COVID-19-related hospitalization. Kaplan-Meier estimators were used to calculate outcome risk overall and across subgroups. Cox proportional-hazards models were used to estimate adjusted hazard ratios (aHR) and 95% confidence intervals (CI).

Results: Of 13,522 patients treated with CAS+IMD, 12,972 were matched to 41,848 untreated patients. The 30-day composite outcome risk was 1.9% (95% CI 1.7-2.2) and 4.4% (95% CI 4.2-4.6) in the treated and untreated cohorts, respectively; treated patients had a 49% lower relative risk of the composite outcome (aHR 0.51; 95% CI 0.46-0.58) and a 67% relative risk of 30-day mortality (aHR 0.33, 95% CI 0.18-0.60). Effectiveness was consistent across vaccination status and various subgroups.

Discussion: Patients with COVID-19 benefitted from treatment with SC CAS+IMD versus untreated patients. The results were consistent across subgroups of patients, including older adults, immunocompromised patients, and patients vaccinated against COVID-19. Results were robust across numerous sensitivity analyses.

Conclusion: SC CAS+IMD is effective in reducing 30-day COVID-19-related hospitalization or mortality in real-world outpatient settings during the Delta-dominant period.