Neutralizing Antibody Responses in COVID-19 Convalescent Sera

Area of Science:

• Immunology
• Virology
• Infectious Diseases

Background:

• Passive antibody transfer via convalescent plasma is an experimental treatment for SARS-CoV-2 infections.
• The US FDA initially recommended a target antibody titer of 160 for convalescent plasma.
• Understanding antibody neutralization kinetics post-COVID-19 recovery is vital for treatment efficacy.

Purpose of the Study:

• To evaluate SARS-CoV-2 neutralizing antibody activity in recovered COVID-19 patients' sera.
• To assess antibody titers at different time points post symptom onset (PSO).
• To determine the correlation between antibody levels and neutralization capacity at varying stringencies.

Main Methods:

• Sera from recovered COVID-19 patients were analyzed using plaque reduction neutralization tests (PRNT).
• Neutralization was assessed at moderate (PRNT50) and high (PRNT90) stringency thresholds.
• Enzyme-linked immunosorbent assay (ELISA) titers were used to categorize antibody levels.

Main Results:

• Neutralizing antibody activity significantly increased with time PSO, peaking between 31-35 days.
• At peak, approximately 93% (PRNT50) and 54% (PRNT90) of sera met the 160 titer threshold.
• High ELISA titers (>960) correlated with maximal neutralization, but not all met FDA recommendations, especially at PRNT90.

Conclusions:

• SARS-CoV-2 neutralizing antibody levels and activity evolve post symptom onset.
• Serum characterization for specific neutralization activity is essential for convalescent plasma therapy.
• Current FDA guidelines may require refinement based on neutralization stringency and time post-infection.