Characterization of cross-reactive but not cross-neutralizing antibodies. (A) K_D for Wuhan-Hu-1 and Gamma RBDs of antibodies from Gamma-infected cohort. Red horizontal bars indicate geometric mean values; no significant difference by two-sided Wilcoxon matched-pairs signed rank test. BLI traces shown in Fig. S2, A and B; mean K_D calculated based on triplicate binding curves matching theoretical fit with R² value ≥ 0.8. (B) Neutralization of Wuhan-Hu-1 pseudovirus by monoclonal antibodies from Wuhan-Hu-1–infected (gray) and Gamma-infected (black) cohorts, summarized as IC₅₀ values. P = 0.0095 by two-sided Mann-Whitney test. (C) Neutralization of Wuhan-Hu-1 (R683G), Gamma (R683G), and Omicron (R683G) pseudovirus by monoclonal antibodies from Gamma-infected cohort, summarized as IC₅₀ values. Lines connect individual antibodies across variants. Dashed line indicates the limit of detection. P = 0.5338 for Wuhan-Hu-1 (R683G) versus Omicron BA.1 (R683G); P = 0.0158 for Wuhan-Hu-1 (R683G) versus Gamma (R683G); and P = 0.0001 for Gamma (R683G) versus Omicron BA.1 (R683G). Statistical significance determined by Friedman’s test followed by Dunn’s multiple comparisons. For A and B, red horizontal bars indicate geometric mean values. Average IC₅₀ values calculated based on duplicate experiments. (D) IC₅₀ values for n = 18 antibodies against indicated mutant SARS-CoV-2 pseudoviruses. Color gradient indicates IC₅₀ values ranging 0 (white) to 1,000 ng/ml (red). Average IC₅₀ values calculated based on duplicate experiments. (E) Schematic of BLI experiment. (F) Bar graph showing percentages of antibodies assigned to each binding class based on BLI epitope binning experiments for n = 28 antibodies each from Wuhan-Hu-1–infected (gray) and Gamma-infected (black) cohorts. Significance (P = 0.0005) determined using Fisher’s test for exact count data.