Rapid colloidal gold immunochromatographic assay for the detection of SARS-CoV-2 total antibodies after vaccination.

An epidemic caused by the severe acute respiratory syndrome coronavirus (SARS-CoV-2) spread globally in just a few months. To prevent the further spread of the virus, millions of people around the world have been vaccinated for COVID-19. Although the plaque reduction neutralization test (PRNT) has become the gold standard method for determining neutralizing antibodies, this method has many limitations; therefore, there remains an urgent need for a quick and accurate technique to evaluate the immune efficacy of COVID-19 vaccines. Here, after the recombinant expression of the SARS-CoV-2 spike protein receptor binding domain (S-RBD), we established a colloidal gold immunochromatographic assay (GICA) based on the principle of a double antigen sandwich for the detection of total antibodies in sera. Under the developed conditions, the GICA was capable of the rapid detection of SARS-CoV-2 total antibodies within 15 min. In addition, the anti-S-RBD antibodies measured by the GICA had a good correlation with the results measured by ELISA, indicating that the GICA may be used as a rapid tool for the detection of neutralizing antibodies derived from SARS-CoV-2 infection. Clinical detection was performed using serum samples obtained from 40 subjects who had received their two doses of the COVID-19 vaccine and 20 unvaccinated serum samples. We found that our method had high sensitivity and specificity; therefore, our convenient and rapid GICA method could preliminarily evaluate the protection rate and effectiveness of vaccines by monitoring total antibody levels.