Evaluation of a new rapid antibody test based on immunochromatography targeting the S protein of SARS-CoV-2: COVID-19 immunity passport based on immunochromatographic test

Abstract

We evaluated the clinical performance of an immunochromatographic antibody test (ICT), namely, a colloidal gold immunochromatography test “NOZOMI^®” for the IgG antibody against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) S protein. We examined 142 serum specimens collected from 92 patients with COVID-19 and also 50 serum specimens collected from febrile non-COVID-19 patients. Additionally, 50 medical staff members who had completed two doses of SARS-CoV-2 vaccines were also included in this study. The sensitivity, specificity, and accuracy for IgG for the S protein were 51.1% (47/92), 96.0% (48/50), and 80.8%, respectively. Among the 50 non-COVID-19 serum specimens, two generated a false-positive result in this ICT “NOZOMI^®”. However, IgG for the S protein was satisfactorily detected in 100.0% (17/17) of specimens collected > 22 days after symptom onset. In case of medical staff members, the IgG-S antibody was quantitatively evaluated using the Elecsys^® Anti-SARS-CoV-2 S RUO antibody test, and the serum specimens determined to have an antibody titer of 500 U/mL or higher also showed a positive result in the ICT test “NOZOMI^®”. Our preliminary data suggest that ICT has potential use in the implementation of the COVID-19 immunity passport.