ABSTRACTMeasurement of antibody content and function after a viral illness is important for diagnosis and selection of the best convalescent plasma (CP) units for passive immunization. Zhang et al. (mBio 14:e03523-22, 2013,https://doi.org/10.1128/mbio.03523-22) analyzed over 19,000 coronavirus disease 2019 (COVID-19) CP (CCP) samples from the early days of the COVID-19 pandemic and reported a moderately strong correlation between antibody amount and neutralizing titer. Strikingly, about one-third of the samples had little or no neutralizing activity. The results provide a detailed glimpse of the humoral immune response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in immunologically naive humans and reveal major differences in the quality of CP units collected for passive therapy before antibody screening. Heterogeneity in CCP quality undoubtedly contributed to the variable therapeutic efficacy. Analysis of the COVID-19 serology data suggest that, for the next infectious disease emergency, the best approach after quick establishment of methods for robust antibody-level stratification would be to use CP units in the top quintile of antibody content and neutralizing capacity.