Fig. 2. Prior history of SARS-CoV-2 infection increases binding to the S1 region of lineage A SARS-CoV-2 relative to those without prior history of infection.

(A and B) Binding of antibodies to lineage A S1 was measured in serum samples isolated from participants after two doses of vaccine without prior infection (A) or with prior infection (B). OD₄₅₀, optical density at 450 nm. (C and D) Binding to the lineage A RBD was also evaluated in serum samples collected after two doses of vaccine without prior infection (C) or with prior infection (D). (E) EC₅₀ titers are shown based on prior history of infection and binding. Because of sample constraints, the two doses with infection group n = 18. The plot in (E) shows mean ± SD. Differences between groups in (E) were evaluated using one-way ANOVA with Tukey’s multiple comparisons test. **P < 0.01; ****P < 0.0001.