Fig. 6: Peptide-based SARS-CoV-2 serodiagnostic ELISA for SARS-CoV-2.

IgG detection in post-SARS-CoV-2-infection sera from children (black, control (n = 20; 10 hospitalized controls and 10 additional nonhospitalized healthy pediatric samples (ages 12–35 months, collected in 2009)); orange, mild/moderate COVID-19 (n = 16); red, severe COVID-19 (n = 10); cyan, mild/moderate MIS-C (n = 2); blue, severe MIS-C (n = 10)) in comparison with 72 pre-COVID influenza-infected adult controls (flu; collected in 2010; gray) are shown on the left, against each protein (a and b), or individual peptides (c–f) or a mixture of four peptides (g), by ELISA using HRP-conjugated anti-human IgG-Fc-specific antibody. Longitudinal analysis of IgG responses to the SARS-CoV-2 proteins and peptides in serum (n = 100) collected at different DPoS from 27 COVID-19 adult patients (shades of red) are shown on the right of each protein/peptide. Dots represent individual serum samples collected at the indicated DPoS, and the samples from the same COVID-19 patients are connected by the lines. Absorbance (y axis) is for 100-fold dilution serum. Cutoff values for each antigen in ELISA were determined by area under the receiver operating characteristic (ROC) curve analysis of the negative controls (using ten control hospitalized children serum samples at 100-fold serum dilution) in GraphPad Prism. The trend line fits were performed for longitudinal adult COVID-19 patients using a nonlinear regression model with polynomial distribution through the origin in GraphPad Prism. The trend line is depicted as the central, colored line with the error bands representing 95% confidence intervals (shaded colored area). Area under the ROC curve analysis using GraphPad Prism was performed to calculate sensitivity (%) and specificity (%) values with 95% confidence intervals. Data are the average values of two experimental ELISA runs. The variation for each sample in duplicate runs was <7%.

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