Figure 1.
Reactivity of prepandemic and COVID-19 serum to coronaviruses spike and to SARS-CoV-2 pseudo-type.
(a) Enzyme-linked immunosorbent assay to SARS-CoV-2 spike antigen with prepandemic human serum (n = 220) showing high cross-reactivity which decreases with increasing fold dilutions. Dotted line shows cut-off for positivity. (b) Enzyme-linked immunosorbent assay to HCoV spike antigens with the prepandemic human serum showing responses among adults (n = 195) and children (n = 431). There were significantly higher responses in adults than children with all HCoV spike antigens except HCoV-NL63 spike. (c) Pseudotyped SARS-CoV-2 neutralization using the selected SARS-CoV-2 spike (S2) reactive IgG (n = 30) and nonreactive IgG (n = 15) samples are shown. There was neutralization with the S2-reactive samples, mean ID50 of 1:251 compared with mean ID50 of 1: 2461 of COVID-19 pooled (C19 pool) convalescent serum used as assay-positive control but no neutralization with S2-nonreactive IgG samples. (d) There were significantly higher IgG responses for HCoV-HKU1 and OC43 for S2-reactive than S2-nonreactive sera but no significant difference for NL63 and 229E.
HCoV, human coronaviruses; Ig, immunoglobulin; ns, not significant; OD,optical density.