RBD binding and neutralizing antibodies in uninfected participants after vaccination. (A) Binding antibody levels to RBD (arbitrary units, AU) and (B) neutralizing antibodies (ID50) in N-antibody seronegative participants vaccinated once (1×) or twice (2×) with Vaxzevria (VX), Comirnaty (COR), or Spikevax (SV). The Kruskal–Wallis test including all five groups indicated significant differences for the RBD and neutralizing antibody levels ((A) p < 0.0001, (B) p < 0.0001, judged at 5% significance level). Pairwise comparisons were performed to (i) compare antibody response to one vaccination between vaccine types (COR vs. VX, SV vs. VX, SV vs. COR), (ii) compare two versus one vaccination (COR-2x vs. COR-1x, SV-2x vs. SV-1x) and (iii) compare two vaccinations of different vaccine types (SV-2x vs. COR-2x). p-values of these pairwise group comparisons with the Mann–Whitney test are shown (judged for significance at a Bonferroni-corrected level of 0.05/6 = 0.008 to account for 6 tests). Dashed lines mark the upper and lower limits of the linear range of the assay.