Anti-SARS-CoV-2 Neutralizing Responses in Various Populations: Use of a Rapid Surrogate Lateral Flow Assay and Correlations with Anti-RBD Antibody Levels.

Background: After the global COVID-19 crisis, understanding post-infectious immunity and vaccine efficacy remains crucial. This study aims to assess anti-SARS-CoV-2 immunity through a quantitative analysis of anti-receptor-binding domain (RBD) antibodies and rapid functional testing of the neutralizing humoral response.
Methods: A retrospective analysis was conducted on samples from various cohorts, including partially vaccinated, fully vaccinated, post-COVID/no-vaccination, and post-COVID/vaccination individuals with various immune-competency statuses. The anti-RBD antibodies were measured using an automated chemiluminescence assay, while the neutralizing antibodies' (NAbs') activity was assessed through the lateral flow ichroma COVID-19 nAb test (LFT), a surrogate neutralization assay.
Results: The analysis revealed various levels of anti-RBD antibodies and seroneutralization responses across cohorts, with the post-COVID/vaccination group demonstrating the most robust protection. A correlation between anti-RBD antibodies and seroneutralization was observed, albeit with varying strength depending on the subgroup analyzed. Longitudinal assessment following natural infection showed an initial surge followed by a decline in both measures. A cutoff of 3.0 log ₁₀ BAU/mL was established to predict significant seroneutralization.
Conclusions: The ichroma™ COVID-19 nAb test displayed high specificity and emerged as a valuable tool for monitoring anti-SARS-CoV-2 immunity. These findings contribute to understand the antibody response dynamics and underscore the potential of rapid tests in predicting protection against SARS-CoV-2 infection.