Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is the RNA virus strain that causes COVID-19, the disease first identified in 2019. Initially designated 2019-nCoV (2019 novel coronavirus), COVID-19 was declared a public health emergency on January 30, 2020, and later declared a worldwide pandemic on March 11, 2020. SARS-CoV-2 spreads through human-to-human transmission and enters human cells through its binding of the angiotensin converting enzyme 2 (ACE2) receptor. Each virion consists of 4 structural proteins: S (spike protein), E (envelope), M (membrane), and N (nucleocapsid). For this assay, the N protein was chosen to maximize the likelihood of antibody detection, since it is the most immunodominant protein in the coronavirus family.

Current research has shown that antibody levels decrease in the serum of COVID-19 patients over time (4) and vary depending on disease severity. In fact, a higher number of asymptomatic participants become seronegative at 60 days indicating a true decline over a 2-month period rather than an artifact of assay performance. Due to this, the current assay had antibody profiles benchmarked to a serum specific anti-N protein assay instead of PCR assay results.