Antibody assays
Recombinant SARS-CoV-2 spike antigens S1, S2, RBD, and spike antigens
from hCOVs- HKU1, OC43, NL63, 229E were purchased from SinoBiological
and nucleocapsid protein (NP) was kindly provided by André Matagne,
University of Liège. All antigens were covalently coupled to fluorescent
magnetic beads (Luminex Corporation) and were used to measure
antigen-specific antibodies using the Fc array assay as described
previously 15. Data was acquired on BioPlex-200
equipment (Bio-Rad) and the results were expressed as median
fluorescence intensity (MFI). See the list of reagents in Supplementary
Table I.