Fig. 2
Human serum binding to SARS-CoV-2 Wuhan original strain, Beta, Delta, and Omicron RBD. A ELISA using sera from hospitalized COVID-19 patients. B ELISA using sera from 2×BNT162b2-vaccinated persons (7–52 days after 2nd immunization). C ELISA using sera from 1×Ad26.COV2.S-vaccinated (14–33 days 1st immunization). D ELISA using sera from 2×mRNA-1273 (5–55 days after 2nd immunization). E ELISA using sera from 2×BNT162b2 or 1× Ad26.COV2.S vaccinated + boosted with BNT162b2 or mRNA-1273 (5–49 days after 3rd or in case of Ad26.COV2.S 2nd immunization) binding to the Omicron variant. F Rearranged representation of the data presented in A–E. The ELISAs were performed as single-point titrations. The software Gen5 version 3.03 was used to calculate EC50 values, further expressed as relative potency in respect to an internal calibrant, for which the Binding Antibody Unit (BAU) was calculated using the WHO International Standard 20/136 titrated on Wuhan wt as reference. The geometrical mean values and the 95% CI are given in the graphs. The graphics and statistical analysis were performed with Graphpad Prism 9.1. For A–E: Friedman test with Dunn’s multiple comparisons test was performed on the four conditions per graph (WT, Beta, Delta, Omicron). For F: Kruskal-Wallis test with Dunn’s multiple comparisons test was performed. Geometric mean and 95% confidence interval are represented by error bars. Multiplicity adjusted P values are shown as follows: ns: P > 0.05, *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001, ****P ≤ 0.0001