A serological assay to detect human SARS-CoV-2 antibodies

OBJECTIVES: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), can lead to severe respiratory illness. Patients with underlying comorbidities have a high risk of contracting COVID-19. Therefore, serological assays are urgently needed to diagnose asymptomatic carriers of SARS-CoV-2, to estimate the prevalence of infection, and for disease prevention and control. This study aimed to develop an enzyme-linked immunosorbent assay (ELISA) for the detection of anti-SARS-CoV-2 antibodies in humans. METHODS: An ELISA test was designed and established to detect antibodies against the SARS-CoV-2 spike protein in serum samples from 41 quantitative reverse transcription polymerase chain reaction (qRT-PCR) - positive hospitalised COVID-19 patients. Forty-two convalescent patients' sera served as positive controls, while 117 pre-pandemic serum samples were used as negative controls. RESULTS: A comparison between different SARS-CoV-2 proteins was performed, which included the full-length spike (S) protein and the S1 and S2 subunits. The full-length S protein showed the strongest reactivity for anti-SARS-CoV-2 IgG antibodies in patients' serum samples. Additionally, since antibodies could be detected at very low concentrations, the assay was found to be sensitive. CONCLUSION: The current assay was specific, since cross-reactions with other SARS coronaviruses and respiratory viruses such as influenza were not found. Additionally, it was highly sensitive, since the test was able to identify antibodies even at very low concentrations. Therefore, this assay has promise as a screening method at the population level and may be used for in future seroepidemiological studies.