Fig 1: ELISA to detect and measure SARS-CoV-2 spike-specific IgG and IgA in COVID-19 convalescent sera.

Serially diluted convalescent patient sera (colored circles) and a pre-2020 negative control (gray diamonds) were added to recombinant SARS-CoV-2 spike protein-coated ELISA plates. Captured IgG (a) and IgA (b) were detected using Ig class-specific secondary antibody-HRP conjugates. Absorbance (A₄₅₀) values were fitted to a sigmoidal curve. Samples were re-analyzed at three dilutions that best characterized the extent of the antibody reactivity for IgG (c) and IgA (d). Averages +/− SD are shown, n=4 from two independent experiments. SD values smaller than the height of the symbols are not shown.