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. 2020 Jun 4;81(3):420–426. doi: 10.1016/j.jinf.2020.05.067

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© 2020 The British Infection Association. Published by Elsevier Ltd. All rights reserved.

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. 2 — Seroprevalence analysis of SARS-CoV-2 with EIA assay and microneutralization assay. (A) The detection of IgM and IgG humoral responses against RBD and NP protein were detected by using sera samples diluted at 1:20 using EIA assay. Dashed blue line indicated cut-off value for each EIA assay, which was determined based on archived serum samples collected before COVID-19 outbreak. Sera from healthy controls (HC) collected in 2019 and the non-COVID-19 pneumonia patients were included as negative control, whereas 60 samples collected at different time points from 20 COVID-19 patients were used as positive control. Serum samples were collected on 14^th day of the quarantine from 105 HCWs and they were also tested to determine IgM and IgG responses for RBD and NP protein. (B) The correlation analysis between anti-NP IgM and OD_450nm-620nm value of anti-RBD IgM (left panel) and the correlation analysis between anti-NP IgG and OD_450nm-620nm value of anti-RBD IgG (right panel). (C) The correlation analysis between the neutralization percentage of serum and anti-NP IgG (left panel) and the correlation analysis between the neutralization percentage of serum and OD_450nm-620nm value of anti-RBD IgG (right panel). OD_450nm-620nm = optical density at 450nm-620nm. NP = nucleoprotein. RBD = receptor-binding domain.