According to a study published in the New England Journal of Medicine, high-titer convalescent plasma if administered early after the onset of COVID-19 resulted in a significant reduction in hospitalizations among the unvaccinated.

Themulticenter, double-blind, randomized, controlled trial, compared the efficacy and safety of Covid-19 convalescent plasma to the control plasma, in symptomatic adults (≥18 years of age). It included 1,225 participants who were randomly assigned to receive either a plasma containing at least 1:320 SARS-CoV-2 anti-spike protein antibody levels (>3.5 arbitrary units at 1:101 dilution in accordance with indication change after March 9, 2021) or control plasma in a single, approximately 250-mL infusion over 1 hour.

The primary outcome (defined as Covid-19–related hospitalization or death within 28 days after transfusion) was observed in 17 of 592 participants (2.9%) who received convalescent plasma and 37 of 589 participants (6.3%) who received control plasma (absolute risk reduction, 3.4 percentage points; 95% confidence interval, 1.0 to 5.8; P=0.005). A relative risk reduction of 54% was seen among most of the unvaccinated participants (53 of 54), with three deaths in the trial occurring in the control group. (MedPage Today March 30, 2022), N Engl J Med 2022; DOI: 10.1056/NEJMoa2119657.