This study states that Seroepidemiological studies are urgently needed to understand the true incidence of coronavirus disease 2019 (COVID-19) and gauge the level of population immunity. Since such studies typically involve screening a large number of sera, the assays of choice should be highly sensitive, high-throughput, and safe. Enzyme-linked immunoassays (EIA), particularly those using recombinant proteins, although less specific than neutralization assays, have the advantage of being high-throughput, safe, and easy to standardize.

The major antibody responses after coronavirus infections are directed against the Spike (S) and Nucleocapsid (N) proteins.1 During Severe Acute Respiratory Syndrome Coronavirus-1 (SARS) infections, anti-N antibodies appeared earlier and were subject to higher cross-reactivity than anti-S antibodies, while anti-S antibodies were better correlated to neutralization activity.2 Aside from the zoonotic origin SARS and Middle-East Respiratory Syndrome (MERS) coronavirus, there are four human strains of coronaviruses (reviewed in3) and seroprevalence to any of these viruses in older adults can be greater than 90%.4 Thus, the COVID-19 serological assays should be sensitive and specific enough to discriminate responses from other coronaviruses.

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