Fig. 4

Comparative analysis of neutralizing antibody responses in uninfected and infected older adults after booster vaccination. a‒c Neutralizing titers against the indicated pseudoviruses in sera collected from uninfected (squares), early infected (infected between days 22‒92, triangles), and later infected (infected between days 93‒185, circles) participants at days 21 (a), 92 (b), and 185 (c) after one-dose booster of the Tri‑XBB.1.5, Bi‑Omi‑XBB, or Tetra‑XBB.1 vaccine. Each square, triangle, or circle represents the individual the 50% neutralization titer (NT₅₀). The vertical bars represent the median and 95% confidence intervals. The geometric mean titers (GMTs) are shown above each group. The dotted line represents the assay detection threshold (NT₅₀ = 30). Statistical comparisons among the three groups were conducted via the Kruskal‒Wallis test with the false discovery rate. A p-value less than 0.05 was considered statistically significant, and only significant differences are displayed in the figure. P-values are denoted as *p < 0.05 and **p < 0.01