Fluctuating High Throughput Serological Assay Results in Recurrent Convalescent Plasma Donors

The clinical and scientific communities rely on serology testing to analyze the degree of antibody-mediated immunity afforded to recovered patients from SARS-CoV-2 infection. Neutralizing antibodies present in COVID-19 convalescent plasma (CCP) remains a practical therapy to treat COVID-19 patients requiring hospitalization. However, it remains unclear how long antibody levels persist in CCP donors after recovery. An accurate estimation of antibody kinetics in CCP donors provide an important observation to further define the extent of long-term immunity in recovered patient and simultaneously inform CCP collection processes in efforts to improve CCP dosing and therapeutic outcome. In this study, we analyzed 63 donors and measured antibody levels using two high throughput screening assays (HTSA) designed to detect antibodies targeting the spike protein (S1) and nucleocapsid protein (NP) of SARS-CoV-2 and monitored antibody levels between 2-8 consecutive donations. We show that anti-S1 antibody levels, as measured using the Ortho Total Ig HTSA, increased over time in repeat CCP donors while anti-NP antibody levels, as measured using the Abbott IgG HTSA, were unchanged or decreased over time. When we normalized these data, we found that both the absolute levels of anti-S1 antibodies and the ratio between S1 and NP antibodies tends to increase over time. These data have important implications for the convalescent donation process, patient protection from future infection and characterization of the SARS-CoV-2 immune response.