Fig. 8: The principle of cross-protection was verified between the various subtypes.

a Mice (n = 5 per group) were immunized i.m. with BV or BY, or i.n. with BY + NVT twice at two-week intervals. Two weeks after the last vaccination, the mice were i.n. challenged with BV virus (B/Shandong/7/97). Body weight and survival were monitored daily. b Mice (n = 5 per group) were immunized i.m. with H3N2 or i.n. with H3N2 + NVT twice at two-week intervals. Two weeks after the last vaccination, the mice were i.n. challenged with canine H3N2 virus (A/canine/VC378/2012). Body weight and survival were monitored daily. c Mice (n = 5 per group) were immunized i.m. with QIV or i.n. with QIV + NVT twice at two-week intervals. Two weeks after the last vaccination, the mice were i.n. challenged with pandemic H1N1 virus (A/Puerto Rico/8/34). Body weight and survival were monitored daily. a–c Weight-loss data are shown as mean value ± SD. Survival data are represented as Kaplan‒Meier survival curves, and the significant differences in survival rates were calculated by the log-rank test. d Mice (n = 20 per group) were immunized i.m. with 2020-2021 season QIV, or i.n. with QIV + NVT twice at two-week intervals. Two weeks after the last immunization, pooled sera and pooled lung cells were used to measure the serum HAI titer and lung CD4⁺ T-cell response to each indicated seasonal influenza vaccine strain. The data are expressed as dot plots, with horizontal lines representing the medians. These experiments were performed once. ns, not significant. Source data are provided as a Source Data file.