Fig. 4: Cross-reactive antibody and B-cell responses to Omicron XBB after bivalent booster vaccination.

A IgG endpoint titres and (B) live virus IC₅₀ titres against XBB spike. The dotted line indicates the limit of detection. Geometric mean titres (GMT) and geometric mean ratios (GMR) are shown above the graph. Asterisk indicates p value of Kruskal–Wallis test with Dunn’s post-test comparing D0 with D7, 14, 28 or 84. C Representative staining of XBB.1.5 spike probe among populations of AN⁺, AN⁺BA.1⁺ or AN^-BA.1⁻ IgG⁺ memory B cells. D Proportion of XBB⁺ cells in Ag⁺ IgG⁺ B cells at baseline and day 28 post-vaccination. Bold lines join the median for each time point. N = 32 at days 0 and 14; N = 31 at day 28 and N = 17 at day 84. B-cell proportions were analysed using a non-parametric paired-sample Wilcoxon signed-rank test. E Correlation between frequencies of BA.1-specific AIM⁺ CD4⁺ Tmem or F frequencies of AN⁺BA.1⁺XBB.1.5⁺ cross-reactive MBC at D0 and neutralisation titres against XBB at D28 post-vaccination (n = 31). Correlation assessed by Spearman r test. **p < 0.01, ***p < 0.001, ****p < 0.0001.