Figure 1.

SARS-CoV-2 IgG response in pre-pandemic unexposed donors and individuals recovered from mild COVID-19. The IgG titre was measured in plasma sample from unexposed donors collected prior to pandemic and the COVID-19 patients up to 5 months of recovery by ELISA using the full length Spike protein and Nucleoprotein. The ELISA curves in serially diluted samples are shown from 6 representative unexposed donors (grey line) and COVID-19 cases (red line) for (A) Spike protein, (B) Nucleoprotein. Area under the curve (AUC) for ELISA quantitation of the IgG binding to (C) Spike protein, (D) Nucleoprotein for 42 unexposed donors and 28 COVID-19 cases inclusive of 6 representative donors of each group shown in panel A and B. (E) Neutralizing antibody quantitation in unexposed donors (n=8) and COVID-19 patients (n=12) after >4 months recovery measured using the SARS-CoV-2 surrogate virus neutralization test. (F) HCoVs Nucleoprotein antigen binding (expressed as OD) assessed by ELISA in unexposed donors (n=42) and COVID-19 recovered patients (n=28). Black bars indicate the geometric mean. Dotted line in panels A-E represent the cut-off of positivity. Statistical comparisons were performed by two-tail Mann-Whitney test. ns: non-significant.