Cohort-Specific Serological Recognition of SARS-CoV-2 Variant RBD Antigens.

Objective: Estimating the response of different population cohorts to new SARS-CoV-2 variants is important to customize measures of control. Our goal was to evaluate how antibodies from sera of infected and vaccinated people recognize antigens expressed by different SARS-CoV-2 variants.

Methods: We compared sera from vaccinated donors and four patient/donor cohorts: Sera from critically ill patients collected 2-7 days and more than 10 days after admission to an intensive care unit, a NIBSC/WHO reference panel of SARS-CoV-2 positive individuals, and ambulatory or hospitalized (but not critically ill) positive donors. Samples were tested with an anti-SARS-CoV-2 ELISA kit coated with SARS-CoV-2 RBD recombinant antigens including mutations present in eleven of the most widespread variants.

Results: Sera from vaccinated individuals exhibited higher antibody binding (<0.001) than sera from infected (but not critically ill) individuals when tested against the wild type (WT) and each of 11 variants' receptor binding domain (RBD). Antibodies' binding to the SARS-CoV-2 antigens of at least 6 variants, including Variants of Concern (VOCs), was reduced in comparison to the WT in vaccinated and non-critically ill convalescence individuals.

Conclusion: Understanding differences between population cohorts in the antibody titers against WT vs variant RBD antigens can help design variant-specific immunoassays for surveillance and evaluation of the epidemiology of new variants.