2.3. Neutralization Assay (sVNT)

The SARS-CoV-2 surrogate virus neutralization test (sVNT) was used as a reference in this study (Cat. No. {"type":"entrez-nucleotide","attrs":{"text":"L00847","term_id":"177436","term_text":"L00847"}}L00847, GenScript, NJ, USA) [32,33] for detecting neutralizing antibodies. This assay was developed by GenScript^® Biotech and is now available commercially as 96-well microplates for large serological screening for neutralizing antibodies targeting the RBD domain of the S1 subunit. Moreover, this assay demonstrated a high correlation with the pseudovirus neutralization test (pVNT, R² = 0.84) and the complete virus-neutralization test (cVNT, R² = 0.85) [33]. Validation of sVNT showed a specificity of 99.9% and a sensitivity of 95.0–100% [33]. In this study, all SARS-CoV-2 RT-PCR- positive plasma samples were tested for neutralizing antibodies against the RBD protein using the sVNT. According to the manufacturer’s instructions, a value result ≥20% signal inhibition was considered positive (neutralizing antibodies were detected), and <20% signal inhibition was considered negative (neutralizing antibodies were not detected).