Evaluation of a novel multiplexed assay for determining IgG levels and functional activity to SARS-CoV-2
The emergence of SARS-CoV-2 has led to the development of new serological assays that could aid in diagnosis and evaluation of seroprevalence to inform an understanding of the burden of COVID-19 disease. Many available tests lack rigorous evaluation and therefore results may be misleading. Objectives: The aim of this study was to assess the performance of a novel multiplexed immunoassay for simultaneous detection of antibodies against SARS-CoV-2 trimeric spike (S), spike receptor binding domain
... ptor binding domain (RBD), spike N terminal domain and nucleocapsid and a novel pseudo-neutralisation assay. Methods: A multiplexed solid-phase chemiluminescence assay (MesoScaleDiscovery) was evaluated for the simultaneous detection of IgG binding to four SARS-CoV-2 antigens and the quantification of ACE-2 binding inhibition (pseudo-neutralisation assay). Sensitivity was evaluated with a total of 196 COVID-19 serum samples (169 confirmed PCR positive and 27 anti-nucleocapsid IgG positive) from individuals with mild symptomatic or asymptomatic disease. Specificity was evaluated with 194 control serum samples collected from adults prior to December 2019. Results: The specificity and sensitivity of the binding IgG assay was highest for S protein with a specificity of 97.4% and sensitivity of 96.2% for samples taken 14 days and 97.9% for samples taken 21 days following the onset of symptoms. IgG concentration to S and RBD correlated strongly with percentage inhibition measured by the pseudo-neutralisation assay. Conclusion: Excellent sensitivity for IgG detection was obtained over 14 days since onset of symptoms for three SARS-CoV-2 antigens (S, RBD and N) in this multiplexed assay which can also measure antibody functionality.