Analysis of presence and short-term persistence of SARS-CoV-2 neutralizing antibodies in COVID-19 convalescent plasma donors

In March 2020, the FDA approved the use of COVID-19 convalescent plasma (CCP) as an investigational new drug for treatment of COVID-19. Since then, collection of CCP from COVID-19 recovered patients has been implemented in several donor centers across the country. Children’s Hospital Colorado rapidly put into practice a CCP collection protocol, necessitating the development and implementation of assays to evaluate SARS-CoV-2 antibodies in CCP units. We evaluated 87 separate units of CCP collected from 36 donors over two to four sequential donations using both antigen- binding assays for SARS-CoV-2 nucleoprotein and spike antigens, and a live virus focus reduction neutralization test (FRNT ₅₀ ). Our data shows that the majority of donors (83%) had a FRNT ₅₀ titer of 1:80 or greater, and 61% had a titer ≥ 1:160, which meet the FDA’s criteria for acceptable CCP units. Additionally, our data indicates that analysis of antibodies to a single SARS-CoV-2 antigen is likely to miss a percentage of seroconverters; however, these individuals tend to have neutralizing antibody titers of <1:80. Of note, there was considerable variability in the short term, sustained antibody response, measured by neutralizing antibody titers, among our donor population.