Performance and utility of an oral fluid-based rapid point-of-care test for sars-cov-2 antibody response following covid-19 infection or vaccination

Analysis of anti-SARS-CoV-2 antibodies can identify recent-onset or prior COVID-19 infection or vaccine-induced humoral immunity. We have developed a rapid point-of-care test for IgG, M, or A-class immunoglobulins that recognize the S1 domain of the SARS-CoV-2 spike protein (CovAb). The test employs a lateral-flow strip design with a recombinant SARS-CoV-2 spike protein S1 domain capture antigen to detect anti-SARS-CoV-2 antibodies in oral fluid samples. Oral fluid samples are collected with a swab that captures the gingival crevicular fluid component of oral fluid that represents a plasma transudate and that is the primary source of oral fluid monomeric antibodies. The sensitivity of the CovAb test is 97.29% and the specificity is 98.13%, and the results obtained are similar to those obtained using matched fingerstick whole blood samples and in an EUA-approved commercial serology test. Oral fluid SARS-CoV-2 antibodies could be detected in subjects more than 7 months post-symptom onset. We also demonstrate the utility of the CovAb test in characterizing adaptive immune responses to vaccination in COVID-19-naive and exposed populations after first and second vaccine doses and show that significant heterogeneity in magnitude of antibody titers achieved is seen after both doses and that prior COVID-19 exposure increases the adaptive immune response to vaccination.