Publication date: Jul 20, 2024

To address the need for novel COVID-19 therapies, we evaluated the fully-human polyclonal antibody product SAB-185 in a phase 3 clinical trial. Non-hospitalized high-risk adults within 7 days of COVID-19 symptom onset were randomized 1:1 to open-label SAB-185 3,840 units/kg or casirivimab/imdevimab 1200 mg. Non-inferiority comparison was undertaken for the pre-Omicron population (casirivimab/imdevimab expected to be fully active) and superiority comparison for the Omicron population (casirivimab/imdevimab not expected to be active). Primary outcomes were the composite of all-cause hospitalizations/deaths and grade ≥3 treatment-emergent adverse events (TEAEs) through day 28. Secondary outcomes included time to sustained symptom improvement and resolution. Enrollment was terminated early due to low hospitalization/death rates upon Omicron emergence. 733 adults were randomized, 255 included in pre-Omicron and 392 in Omicron analysis populations. Hospitalizations/deaths occurred in 6 (5. 0%) and 3 (2. 2%) of pre-Omicron SAB-185 and casirivimab/imdevimab arms, respectively (absolute difference [95% CI] 2. 7% [-2. 3%, 8. 6%]), inconclusive for non-inferiority; and 5 (2. 5%) versus 3 (1. 5%) (absolute difference 1. 0% [-2. 3%, 4. 5%]) for Omicron. Risk ratios for grade ≥3 TEAEs were 0. 94 [0. 52, 1. 71] (pre-Omicron) and 1. 71 [0. 96, 3. 07] (Omicron). Time to symptom improvement and resolution were shorter for SAB-185, median 11 vs 14 (pre-Omicron) and 11 vs 13 days (Omicron) (symptom improvement), and 16 vs 24 days and 18 vs >25 days (symptom resolution), p

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