UCLA

Objectives: Despite extensive research on the blood neutralizing antibodies (NAbs) to SARS-CoV-2, relatively little is known about the level of saliva NAbs and how it relates to systemic NAb levels. Current emergency use authorization (EUA) serology assays only include measuring NAbs in plasma or serum and there is no test for measuring NAbs in saliva. The aim of this study was to develop a saliva-based assay for measuring COVID-19 NAbs and compare the level of NAbs in saliva and plasma.Methods: The EFIRM (Electric Field Induced Release and Measurement) technology, is a novel platform that can quantify target molecules in both blood and saliva. The EFIRM NAb assay was developed using human angiotensin-converting enzyme 2 (hACE2) protein immobilized onto a gold electrode. The protein-protein interaction between the virus receptor binding domain (RBD) and hACE2 is disrupted by NAbs against SARS-CoV-2 RBD, if present in a clinical sample. Paired plasma and saliva samples collected from COVID-recovered or vaccinated patients were assayed for EFIRM NAb. Saliva and plasma samples collected prior to 2019 from a healthy cohort were used to determine the clinical specificity and cutoff. Results: The EFIRM saliva NAb assay detected NAbs in saliva with a limit of detection (LOD) of 31.6 U/mL and differentiated between COVID-19-recovered or vaccinated patients (n = 31) and healthy individuals (n = 60) with an area under the curve (AUC) of 0.923 (95% CI: 0.869 to 0.976), a sensitivity of 87.10%, and a specificity of 86.67%. Comparing the level of neutralizing antibodies in paired saliva and plasma, a significant correlation was seen between neutralizing titers (r = 0.75, p < 0.0001). Conclusion: A quantitative, non-invasive electrochemical saliva-based assay with sufficient sensitivity and specificity was developed to measure SARS-CoV-2 functional neutralizing antibodies. Our novel EFIRM NAb saliva test represents a significant technological advancement to address the unmet clinical needs for large-scale surveillance in the pandemic world and beyond with great potential future applicability.