Phase 2 dose-ranging study of the virologic efficacy and safety of the combination COVID-19 antibodies casirivimab and imdevimab in the outpatient setting
Authors: Portal-Celhay Cynthia , Forleo-Neto Eduardo , Eagan Will , Musser Bret J , Davis John D , Turner Kenneth C , Norton Thomas , Hooper Andrea T , Hamilton Jennifer D , Pan Cynthia , Mahmood Adnan , Baum Alina , Kyratsous Christos A , Kim Yunji , Parrino Janie , Kampman Wendy , Roque-Guerrero Lilia , Stoici Roxana , Fatakia Adil , Soo Yuhwen , Geba Gregory P , Kowal Bari , DiCioccio A Thomas , Stahl Neil , Lipsich Leah , Braunstein Ned , Herman Gary A , Yancopoulos George D , Weinreich David M ,   Study Investigators
Published: November 2021

SummaryBackgroundThe monoclonal antibody combination casirivimab and imdevimab (REGEN-COV®) reduced viral load, hospitalisation, or death when administered 1:1 as an intravenous (IV) dose ≥1200 mg in a phase 3 COVID-19 outpatient study. Availability of subcutaneous (SC) and/or lower IV doses should increase accessibility and/or drug supplies for patients.MethodsThis is a double-blind, placebo-controlled study of SARS-CoV-2-infected outpatients who were asymptomatic, or symptomatic but without risk factors for severe COVID-19. Patients were randomised to single IV dose (517 patients) of REGEN-COV 300, 600, 1200 or 2400 mg or placebo; or a single SC dose (286 patients) of REGEN-COV 600 or 1200 mg or placebo. The primary endpoint was time-weighted average daily change from baseline (TWACB) in viral load from day 1 (baseline) through day 7 in patients seronegative to SARS-CoV-2 at baseline.FindingsAll REGEN-COV treatments showed significant (p<0·001 versus pooled placebo) virologic reduction through day 7. Least-squares mean differences in TWACB viral load for the treatments versus placebo ranged from –0·56 to –0·71 log10 copies/mL. Each REGEN-COV treatment showed significant (p<0·001 versus pooled placebo) and similar virologic reduction through day 7. There were no safety concerns, dose-related safety findings, grade ≥2 infusion related/hypersensitivity reactions, grade ≥3 injection-site reactions, nor fatalities. Two serious adverse events not related to COVID-19 or the study drug were reported.InterpretationIn asymptomatic and low-risk symptomatic SARS-CoV-2-infected outpatients seronegative for antibodies against SARS-CoV-2 at baseline, REGEN-COV significantly and comparably reduced viral load at all IV and SC doses.FundingRegeneron Pharmaceuticals, Inc. and Hoffman-La RocheRESEARCH IN CONTEXTEvidence before this studyEarly phase 1/2 data in coronavirus disease 2019 (COVID-19) outpatients (NCT04425629) found that the REGEN-COV® antibody combination, casirivimab and imdevimab, administered 1:1 as a single intravenous (IV) dose of 2400 mg or 8000 mg significantly reduced viral load over the first week compared to placebo. Enhanced viral clearance was more pronounced in patients who were seronegative for antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), or who had high viral load at baseline. The phase 3 portion of this outpatient treatment study subsequently evaluated 1200 mg IV and 2400 mg IV doses, demonstrating consistent virologic efficacy, further demonstrating that REGEN-COV treatment reduced risk of COVID-19-related hospitalisation or all-cause death, and shortened time to symptom resolution. Virologic clearance was similar among those treated with any of the three doses (8000 mg, 2400 mg, or 1200 mg); therefore, maximal virologic efficacy may have been achieved at the 1200 mg dose in this treatment setting. These results warranted investigation of lower dose regimens.Added value of this studyThe present dose-ranging study evaluated whether a lower dose regimen could demonstrate virologic efficacy similar to that observed with 1200 mg IV and 2400 mg IV doses in outpatient treatment study. Exploration of a wider dose range will provide further characterisation of the clinical effects of REGEN-COV. Moreover, identifying a lower efficacious dose could bolster the ability to provide an adequate therapeutic supply of REGEN-COV in the setting of a global pandemic. A 1200 mg subcutaneous (SC) dose of REGEN-COV also prevented COVID-19 in household contacts of SARS-CoV-2-infected individuals (NCT04452318). The availability of a SC regimen could improve access for patients who have confirmed SARS-CoV-2 infection but for who IV infusion is not feasible.Implications of all the available evidenceDespite the growing number of therapeutics with authorisation or approval for the treatment and/or prevention of COVID-19, there remains a significant global need for effective COVID-19 therapies. Additional therapeutics and dosing regimens will be required to meet demand and to meet the needs of specific patient populations. Lower IV doses of REGEN-COV, and the option of SC administration, should increase accessibility for patients. This increased availability needs to be weighed against several unanswered questions, including 1) whether the correlation between decreased viral load in the nasopharynx and improvement in clinical outcome holds at lower doses of REGEN-COV, and 2) whether the reduced drug exposure margins are sufficient to prevent viral escape and emergence of variants of concern.