RBD IgG ELISAs were performed using a previously published protocol (47 (link)), except that plasma was diluted to a final concentration of 1:20. Human AB serum (Innovative Research) purchased before the COVID-19 pandemic was used as a negative control, and a commercially available rabbit anti-SARS-CoV-2 spike monoclonal antibody (catalog number 40150-R0907, Sino Biological) and donkey anti-rabbit IgG secondary antibody (Jackson ImmunoResearch) were used as a positive control. The plates were read in a VersaMax tunable microplate reader (Molecular Devices). The average of the negative control readings plus 3 times the standard deviation was used as a cut-off for positivity.
N IgG ELISAs were performed using the Elecsys Anti-SARS-CoV-2 immunoassay (Roche) on a Cobas e411 analyzer (Roche) per the manufacturer’s instructions (48 (link)). A COI value >1 was considered positive.
N IgG ELISAs were performed using the Elecsys Anti-SARS-CoV-2 immunoassay (Roche) on a Cobas e411 analyzer (Roche) per the manufacturer’s instructions (48 (link)). A COI value >1 was considered positive.
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