Comparison of two assays to detect IgG antibodies to the receptor binding domain of SARS-CoV-2 as a surrogate marker for assessing neutralizing antibodies in COVID-19 patients

Background: Neutralizing antibodies (NAbs) are important for protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reinfection. In this study, two assays that are correlated with NAbs were compared: the haemagglutination test (HAT) and the surrogate virus neutralization test (sVNT). Methods: The specificity of the HAT was compared with the sVNT, and the sensitivity and persistence of antibodies in patients with varying severity of illness was assessed in a cohort of 71 patients at 4-6 weeks and 13-16 weeks. The kinetics were assessed in the first, second, and third weeks in patients with varying severity of acute illness. Results: The specificity of the HAT was 0.0 0 01). Patients with moderate and severe illness had higher HAT titres when compared to those with mild illness. Six of seven patients with severe illness had a titre of 1:640 during the second week of illness, whereas only five of 31 patients with a mild illness had a titre of > 1:160 in the second week of illness. Conclusions: Since the HAT is a simple and very cheap assay to perform, it would be ideal to use as an indicator of NAbs in resource-poor settings. (c) 2021 The Authors. Published by Elsevier Ltd on behalf of International Society for Infectious Diseases. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )

Automated summary

This study compared two assays correlated with neutralizing antibodies in patients with different severity of illness and found that HAT is a more accurate method for detecting antibody levels. Using HAT as an indicator of neutralizing antibodies in resource-poor settings would be an ideal choice.