Fig. 1: MultiCoV-Ab, a sensitive and specific tool to monitor SARS-CoV-2 antibody responses.

a Control sera (blue, n = 72) and sera from individuals with PCR-confirmed SARS-CoV-2 infection (red, n = 205) were screened in a multiplex bead-based assay using Luminex technology (MultiCoV-Ab) to quantify IgG or IgA responses to various antigens. Reactivity towards trimeric SARS-CoV-2 spike protein (Spike Trimer) or SARS-CoV-2 receptor binding domain of spike (RBD) was found to be the best predictor of SARS-CoV-2 infection. Data are presented as Box-Whisker plots of a sample’s median fluorescence intensity (MFI) on a logarithmic scale. Box represents the median and the 25th and 75th percentiles, whiskers show the largest and smallest values. Outliers determined by 1.5 times IQR of log-transformed data are depicted as circles. Cut-off values for classification for single antigens are displayed as horizontal lines (Spike Trimer IgG: 3,000 MFI, IgA: 400 MFI; RBD IgG: 450 MFI, IgA: 250 MFI). b Sample set from a, was used to compare assay performance of the MultiCoV-Ab using Spike Trimer and RBD antigens with commercially available single analyte SARS-CoV-2 IVD assays which detect total Ig (Elecsys Anti-SARS-CoV-2 (Roche); ADVIA Centaur SARS-CoV-2 Total (COV2T) (Siemens Healthineers)) or IgG (Anti-SARS-CoV-2-ELISA - IgG (Euroimmun)) or IgA (Anti-SARS-CoV-2-ELISA - IgA (Euroimmun)). SARS-CoV-2 infection status of samples based on PCR diagnostic is indicated as SARS-CoV-2 positive or negative. Antibody test results were classified as negative (blue), positive (red), or borderline (gray) as per the manufacturer’s definition. Only samples with divergent antibody test results are shown. c Performance and specifications as stated in the manufacturer’s IVD assay manual. For the manufacturer sensitivity specification, information for samples >14 days post-infection are presented. Respective sensitivity and specificity values calculated in this study are given with 95% Clopper-Pearson confidence intervals⁵². Positive and negative predictive values (PPV/NPV) were calculated based on a seropositivity of 3%. Source data are provided as a Source Data file.