Characterization of SARS-CoV-2 Antibody Titers in over 6,000 Blood and Plasma Donations

Background/Case Studies: Neutralizing antibodies to SARS-CoV-2 are believed to have a Spike protein specificity, specifically to the Receptor Binding Domain of Subunit 1 (S1-RBD) The correlation between disease severity and antibody titers is not presently known This study compared the SARS-CoV-2 antibody titers of recovered COVID-19 patients and non-COVID-19 convalescent plasma (CCP) donors at a single blood center Study Design/Methods: Those presenting to donate CCP were required to provide evidence of having COVID-19, as outlined in the FDA guidance for Investigational COVID- 19 Convalescent Plasma (latest update 05/01/20) which also recommended a neutralizing antibody titer of at least 160 Repository specimens were collected from these donors for testing of antibody titers A laboratory developed test utilizing a S1-RBD total immunoglobulin kinetic-enzyme linked immunosorbent assay (k-ELISA) was used to determine the concentration of antibodies The k-ELISA utilized a standard curve created from a pool of 100 CCP donors to calculate a titer by testing a single dilution of each specimen Non-CCP blood donors were tested with a commercial high throughput qualitative assay for antibodies to S1 of SARS-CoV-2 and reactive specimens were reflexed for titer determination with the k-ELISA Testing was performed on donations collected from April 6, 2020 to July 29, 2020 for CCP donors and May 18th, 2020 to July 29, 2020 for non-CCP blood donors Results/Findings: There were 6,047 donations tested: 34% from CCP donors and 66% from non-CCP donors that tested reactive by the commercial qualitative assay The titer distribution is presented in the Table Non- Reactive results were observed in both CCP and non- CCP donors Titers of the reactive donors were evaluated and gave the following results: mean titer for CCP and non-CCP donors was 1,117 and 858, respectively, the median titer of both groups was 640 The percentage of reactive donors with a titer of ≥160 was 95% (1,785) and 89% (3,170) for CCP and non-CCP donors, respectively There is a statistically significant difference in the titer distribution of the two groups (p<0 0001) Conclusions: At this blood center, CCP donors had a statistically significantly higher titer than non-CCP blood donors, however the median of all reactive donors from both groups was the same and exceeded the recommendations in the FDA Guidance While the allogenic non-CCP donor population had a higher percentage of donors who were non-reactive or with lower titers (< 80), the larger number of this population having titers of ≥160 if successfully recruited to CCP donations would be a valuable source of CCP to help fulfill hospital requests