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Threshold at maximal Youden Index. Individual data points for SARS-CoV-2 positive and negative samples are plotted for IgG, IgA and IgM. Data is shown for all samples and for 8–14 days, 15–21 days or > 21 days from symptoms onset. Dashed lines show OD value at maximal Youden index as calculated from ROC curves shown in Fig. 9.
