Quantifying Anti-SARS-CoV-2 Antibodies

To quantify anti-SARS-CoV-2 antibodies, indirect ELISA was performed as previously described [25 (link)] with the following modifications: ELISA plates (Nunc) were coated with 2.0 μg/mL RBD, S protein, or N protein (Sino Biological) in sodium bicarbonate buffer. Plates were read on a SpectraMax iD3 (Molecular Devices) plate reader. Absorbance readings three standard deviations above the mean day 0 value were considered positive, and titres were reported as the highest serum dilution above this cut-off value. To quantify neutralizing antibodies, microneutralization assays were performed using hamster serum as previously described [23 (link)].