BackgroundOutpatient COVID-19 monoclonal antibody (mAb) treatment via subcutaneous delivery, if effective, overcomes the logistical burdens of intravenous administration.MethodsACTIV-2/A5401 was a randomized, masked placebo-controlled platform trial where participants with COVID-19 at low risk for progression were randomized 1:1 to subcutaneously administered BMS-986414 (C135-LS) 200 mg, plus BMS-986413 (C144-LS) 200 mg, (BMS mAbs), or placebo. Coprimary outcomes were time to symptom improvement through 28 days; nasopharyngeal SARS-CoV-2 RNA below the lower limit of quantification (LLoQ) on days 3, 7, or 14; and treatment-emergent grade 3 or higher adverse events (TEAEs) through 28 days.ResultsA total of 211 participants (105 BMS mAbs and 106 placebo) initiated study product. Time to symptom improvement favored the active therapy but was not significant (median 8 vs 10 days, P=0.19). There was no significant difference in the proportion with SARS-CoV-2 RNA ConclusionsWhile safe, the BMS mAbs delivered subcutaneously were not effective at treating COVID-19 at low risk for progression. The lack of clinically significant activity may relate to the pharmacokinetics of subcutaneous administration of mAbs.