Fig. 1.

Protection by humoral immune responses in individuals with prior Omicron infection. (A) Demographic characteristics of individuals previously infected with Omicron BA.1/BA.2/BA.5 and those not infected with SARS-CoV-2, as well as the infection status in December 2022. Continuous variables were shown in median (interquartile ranges) and categorical variables were summarized as counts (percentages). (B) The efficacy of the prior Omicron infections in preventing the ongoing epidemic of BA.5/BF.7 compared to previously uninfected individuals. The efficacy was estimated by the formula 100 × (1 − IRR), where IRR is the calculated ratio of incidence in the prior Omicron infection group to that in the control group with Bayesian beta-binomial model. (C) Plasma 50% neutralization titres (NT₅₀) against SARS-CoV-2 D614G, BA.5, and BF.7 pseudovirus in those infected with prior BA.1 and reinfection (n = 18) and infected with prior BA.1 without reinfection (n = 34). The geometric mean titres are labeled, and dashed lines show the detection limits (NT₅₀ = 10). Statistical significance was determined by a two-tailed Mann–Whitney test. (D) Plasma 50% neutralization titres (NT₅₀) against SARS-CoV-2 D614G, BA.5, BF.7, BQ.1.1, CH.1.1, and XBB.1.5 pseudovirus in those infected with prior BA.5 without reinfection (n = 26). Plasma samples were collected approximately 3 months before the pandemic (1 month after prior infection). The geometric mean titres are labeled, and dashed lines show the detection limits. (E) Cumulative incidence of reinfection in previously BA.1-infected individuals (n = 52), stratified on plasma NT₅₀ against BF.7 subvariant above or below the threshold calculated by the ROC curve in Fig. S4. HRs (95% Confidence Intervals) from Log-rank test and aHR standed for adjusted HR from Cox regression model after adjustment with age, gender and vaccination. (F) Plasma 50% neutralization titres (NT₅₀) against SARS-CoV-2 D614G, BA.5, BF.7, BQ.1.1, CH.1.1, and XBB.1.5 pseudovirus in those infected with BF.7 (n = 30). Plasma samples were collected approximately 1 month after prior infection. The geometric mean titres are labeled, and dashed lines show the detection limits (NT₅₀ = 10).