Figure E2.

Non-neutralizing strain-specific antibody response. Antibody binding to spike protein (S1, left) and receptor-binding domain (RBD) of spike protein (right) of the B.1 (Wuhan), B1.1.617.2 (Delta), and B.1.1.529 (Omicron) were measured. We compared the binding of patient serum (20 weeks on the anti-SARS-CoV-2–containing subcutaneous immunoglobulin) and serum of five mRNA-vaccinated (B.1 vacc.) subjects collected 4 weeks after the second dose of an mRNA vaccine (Spikevax, Moderna) and of five subjects with Omicron breakthrough infection despite two doses of an mRNA vaccine (B.1 vacc. + B.1.1.529). Receptor-binding domain IgG is considered a surrogate for virus neutralization, and total anti-S1-IgG also contains non-neutralizing antibodies. Data indicate cross-reactive anti-S1-IgG that recognize Omicron in all tested subjects, whereas only Omicron breakthrough infection is associated with high anti-RBD-IgG against Omicron. MFI, median fluorescence intensity.