SARS-CoV-2 antibody levels associated with reduced hospitalization risk remain undefined. Our outpatient COVID-19 convalescent plasma (CCP), placebo-controlled trial observed SARS-CoV-2 antibody levels decreasing 22-fold from matched donor units into post-transfusion seronegative recipients. Unvaccinated recipients were jointly stratified by a) early or late transfusion (≤ 5 or >5 days from symptom onset) and b) high or low post-transfusion SARS-CoV-2 antibody levels (< or ≥ geometric mean). Early treatment with high post-transfusion antibody levels reduced hospitalization risk-0/102 (0%) compared to all other CCP recipients-17/370 (4.6%; Fisher exact p=0.03) and to all control plasma recipients-35/461 (7.6%; Fisher exact p=0.001). A similar donor upper/lower antibody level and early late transfusion stratified analyses indicated significant hospital risk reduction. Pre-transfusion nasal viral loads were similar in CCP and control recipients regardless of hospitalization outcome. Therapeutic CCP should comprise the upper 30% of donor antibody levels to provide effective outpatient use for immunocompromised and immunocompetent outpatients.
Keywords: COVID-19; convalescent plasma; hospitalization; outpatients; randomized controlled trial; virus load.