Neutralizing Antibody Responses in COVID-19 Convalescent Sera
William T Lee, Roxanne C Girardin, Alan P Dupuis, II, Karen E Kulas, Anne F Payne, Susan J Wong, Suzanne A. Arinsburg, Freddy T. Nguyen, Damodara Rao Mendu, Adolfo Firpo-Betancourt, Jeffrey S. Jhang, Ania Wajnberg, Florian Krammer, Carlos Cordon-Cardo, Sherlita Amler, Marisa Montecalvo, Brad Hutton, Jill Taylor, Kathleen A McDonough. The Journal of Infectious Diseases 2020-10-26
Passive transfer of antibodies from COVID-19 convalescent patients is being used as an experimental treatment for eligible patients with SARS-CoV-2 infections. The United States Food and Drug Administration’s (FDA) guidelines for convalescent plasma initially recommended target antibody titers of 160. We evaluated SARS-CoV-2 neutralizing antibodies in sera from recovered COVID-19 patients using plaque reduction neutralization tests (PRNT) at moderate (PRNT50) and high (PRNT90) stringency thresholds. We found that neutralizing activity significantly increased with time post symptom onset (PSO), reaching a peak at 31–35 days PSO. At this point, the number of sera having neutralizing titers of at least 160 was approximately 93% (PRNT50) and approximately 54% (PRNT90). Sera with high SARS-CoV-2 antibody levels (>960 enzyme-linked immunosorbent assay titers) showed maximal activity, but not all high-titer sera contained neutralizing antibody at FDA recommended levels, particularly at high stringency. These results underscore the value of serum characterization for neutralization activity.