We conducted four rounds of testing using rNP as the target analyte, followed by one round using pooled NP positive swab samples from donors. The first round used the best-available-at-the-time rNP analyte, sourced from GeneMedi (GMP-V-2019nCoV-N002), at 50 ng/mL. The second through fourth rounds used a higher-affinity rNP analyte, sourced from Acro Biosystems (NUN-C5227), at 50, 25, and 10 ng/mL, respectively. The third and fourth rounds eliminated antibody pairs that performed poorly in the previous round and added new pairs as antibodies became commercially available. In other words, antibody pair combinations varied round-by-round. A complete list of pairs from all rounds is in Table .