Serological assays
® SARS-CoV-2
Anti-SARS-CoV-2 antibodies were detected using commercial assays that use either SARS-CoV-2 Spike protein or SARS-CoV-2 Nucleocapsid antigens. All assays were used as per the manufacturer’s recommendations.For the main analysis of this study, S-IgG of all 1411 samples was measured using DiaSorin’s LIAISON® SARS-CoV-2 TrimericS chemiluminescence immunoassay as described previouslyFor the main analysis of this study, NC-IgG of all 1411 samples was measured using the Euroimmun anti-SARS-CoV-2-NCP-ELISA. Serum samples were tested on the automated system Euroimmun Analyzer I according to the manufacturer’s recommendations. Results were indicated as Signal-to-Cutoff ratio (S/CO) values. That is, a cutoff value was established, and results were interpreted as a ratio to this cutoff value. S/CO values were interpreted as positive (S/CO ≥ 1.1), borderline (S/CO ≥ 0.8 < 1.1), and negative (S/CO < 0.8). For validation of this assay, positive percent agreement (PPA) and negative percent agreement (NPA) with serological assays used at the other study sites were determined. PPA and NPA with (i) Abbott’s Architect SARS-CoV-2 IgG assay (