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Serum samples collected retrospectively during longitudinal SARS-CoV-2 PCR surveillance were tested by commercial and laboratory serologic assays. Laboratory-based Enzyme Linked Immunosorbent Assay (ELISA) and RadioImmunoAssays (RIA) assessed binding of IgG against recombinant RBD and Spike (Sino Biologics) and nucleocapsid antigen (manufactured in house, courtesy of B. Geiss).
