SARS-CoV-2 IgG antibodies in COVID-19 convalescent plasma and conventional plasma units

The Association for the Advancement of Blood and Biotherapies guidelines recommend the use of high-titer COVID-19 convalescent plasma (CCP) for patients with SARS-CoV-2 at high risk of disease progression, including those who are immunocompromised. We hypothesized that conventional plasma units have comparable neutralizing antibody levels to CCP.

Conventional plasma and CCP units were obtained from blood suppliers. Quantitatively measured antibodies to SARS-CoV-2 were assessed using the MesoScale Discovery multiplex electrochemiluminescence immunoassay. Binding antibody distributions were compared with Wilcoxon rank-sum tests. SARS-CoV-2 neutralizing antibodies were analyzed using the GeneScript ELISA-based neutralization assay. The proportion of conventional and CCP units with a percent signal inhibition of ≥80% (as defined by the United States Food and Drug Administration for CCP in 2021) and exact binomial confidence intervals (CIs) were calculated.

Among 218 conventional plasma units and 74 CCP units collected between September 2023 and July 2024, the distribution of total antibody binding levels largely overlapped between conventional plasma and CCP, though statistically significant differences in median nucleocapsid and spike Omicron variant concentrations were observed. Median percent signal neutralization was 97.5% (range 3.4%-98.6%) among conventional plasma units and 97.7% (range 95.4%-98.6%) among CCP units. For conventional plasma, 95.0% (95% CI = 91.2%-97.5%) met the neutralization antibody threshold for high-titer CCP. For CCP, 100% (95% CI = 95.1%-100.0%) met the neutralization threshold for high-titer CCP.

Conventional plasma units demonstrate similar median antibody concentration to CCP units. In countries or regions where licensed CCP is unavailable and titers are unknown, transfusion of multiple conventional plasma units may be of clinical utility.