Convalescent plasma for COVID-19: Donor demographic factors associated high neutralising antibody titres

Background: Convalescent plasma containing high levels of SARS-CoV-2 antibodies has been studied as a possible treatment for COVID-19. Better understanding of predictors of high antibody levels is needed for improving supply of high-quality therapeutic plasma. Aims: We have evaluated demographic and clinical factors associated with the probability of a convalescent plasma donor having high SARS-CoV-2 IgG antibody levels. Methods: A total of 29,585 convalescent plasma donors employed during the first and second waves of the COVID-19 pandemic in England were included in this study. All had been tested for SARS-CoV-2 IgG antibodies by EUROimmun ELISA. A multivariable logistic regression model was used to quantify the association of the demographic and clinical factors with high (EUROimmun S/Co>6.0) SARS-CoV-2 IgG antibody level. Results: Most of the donors were male (23,024; 78%), with white ethnic background (24,598;83%) and had not been tested for SARS-CoV-2 (15,266; 52%).Overall, less than 20% of convalescent plasma donors with confirmed or suspected SARS-CoV-2 infection harboured high SARS-CoV-2 antibody levels (n = 4,978). We found that older male donors who had been hospitalised with COVID-19 were most likely to harbour high levels of antibodies. White donors were less likely to have high SARS-CoV-2 antibody levels than donors with Asian orblack ethnic backgrounds residing in affluent areas likely reflecting ethnic inequality previously associated with SARS-CoV-2 infection. Discussion: In a time of great uncertainty, and predicted new waves associated with newly emerging SARS-CoV-2 variants, these results will help us to target future convalescent plasma collections.