Fig. 1: RBD-IgG and NP-IgG levels in unvaccinated or vaccinated individuals who previously recovered from COVID-19.

a Schematic diagram representing the sequential order and time scale of the natural infection and vaccination groups. The black virus particle denotes recovery from COVID-19, the gray syringe represents a dose of vaccine, and the blue-capped vial represents blood sample collection. Months were calculated based on the time of the final dose of vaccination. b Comparison of the RBD-IgG and NP-IgG titers of patients receiving one, two, or three vaccine doses in the hybrid-immunity group at 1–3 months post vaccination. c Distribution of RBD-IgG and NP-IgG titers in the infection-only and hybrid-immunity groups. Changes in the distribution of RBD-IgG and NP-IgG titers at 1–3, 4–6, 7–9, and 10–12 months are shown, and darker colors indicate higher titers. d Alteration of RBD-IgG and NP-IgG titer responses over time in the hybrid-immunity group, with the infection-only group serving as a control. e RBD-IgG titers were positively correlated with NP-IgG titers (n = 448). f–h No correlation between RBD-IgG titers and disease severity (f), age (g) or sex (h) was detected. Error bars in b, d, f, and h show the GMT values with 95% confidence intervals, and the colored numbers in the figures represent GMT values. Statistical significance in b, d, and f was analyzed using the Kruskal–Wallis test. Only groups with significant differences are marked in f. Statistical significance in h was analyzed using the paired t-test. Scatter plots in e and g denote the simple linear fit with 95% confidence bands, together with the Spearman correlation coefficient and 2-tailed P value. M, months; MPV, months post vaccination.