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. 2021 Aug 6;39(39):5688–5698. doi: 10.1016/j.vaccine.2021.07.098

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© 2021 The Author(s)

Since January 2020 Elsevier has created a COVID-19 resource centre with free information in English and Mandarin on the novel coronavirus COVID-19. The COVID-19 resource centre is hosted on Elsevier Connect, the company's public news and information website. Elsevier hereby grants permission to make all its COVID-19-related research that is available on the COVID-19 resource centre - including this research content - immediately available in PubMed Central and other publicly funded repositories, such as the WHO COVID database with rights for unrestricted research re-use and analyses in any form or by any means with acknowledgement of the original source. These permissions are granted for free by Elsevier for as long as the COVID-19 resource centre remains active.

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Fig. 4 — Semi-quantitative analysis of serum from SARS-CoV-2 infected and recovered individuals. Graphical representation of serially diluted SARS-CoV-2 positive samples with high and low % neutralization. An optimal dilution series starting from a 1:10 dilution of serum in sample buffer that is mixed equally with RBD-HRP (for a final dilution of 1:20) followed by up to five, serial 1:3 dilutions (ie: 1:20, 1:60, 1:180, 1:540, 1:1620, 1:4860) permits quantification of samples with both high and low neutralizing antibody titers assuring at least one dilution within the linear quantitative range. Graphical representation of OD450 versus log dilution factor for three low (A) and high (B) neutralizing antibody titers. Also represented are the plots of the converted % neutralization versus log dilution factor for the same low (C) and high (D) neutralization samples. Circled points are within the linear range for standard curve interpolation (Fig. 3D). The % recovery between two points within the linear range was examined for samples 8029054639 and 8029054652 (Fig. 4B) and were found to be within 40% of expected as predicted by the inhibitory effect of serum matrix on antibody-antigen interactions [48], [49].