Evaluation of the accuracy in the mucosal detection of anti-SARS-CoV-2 antibodies in nasal secretions and saliva.

COVID-19 vaccination with mRNA vaccines induces immune responses capable of neutralizing SARS-CoV-2. Commercially available serological anti-SARS-CoV-2 quantitative and neutralizing assays are essential for the determination of immune responses to vaccines. Nevertheless, at present there is a lack of validated tests to assess the mucosal response to COVID-19 vaccination and standardized analytic and pre-analytic methods have not yet been defined. The aim of our study was to evaluate the accuracy of two diagnostic immunoassays for COVID-19 (ELISA for IgA-S1 and chemiluminescent assay for IgG-RBD) on serum, saliva, and nasal secretions, by the enrollment of three study populations (healthy controls, vaccinated subjects, and subjects recovered from COVID-19 infection). In order to obtain an appropriate cut-off value for the biological matrices studied, ROC curve analyses were performed. Data demonstrate that the analytical and pre-analytical method we have developed can provide accurate and reliable results for the detection of anti-SARS-CoV-2 mucosal specific antibodies (IgA-S1 and IgG-RBD) on saliva and, as a novelty, on nasal secretions, either after COVID-19 infection or in vaccinated subjects.