Pathogenicity of four H5N6 viruses in mice and replication of RY6 and RY6-160 T in mice. Mean weight of mice infected from 103.0 EID50/50 μL to 107.0 EID50/50 μL of RY6 (A), RY6-160T (B), RHX (E) and RHX-160A (F) (n = 5). Survival rate of mice infected with RY6 (C), RY6-160T (D), RHX (G) and RHX-160A (H); mice were humanly killed when they lost ≥ 25% of their initial body weight. (I and J) Six-week-old SPF BALB/c mice (three/group) were inoculated intranasally with 106 EID50 of RY6 and RY6-160T, and organs were collected on days 3 and 5 post-infection for virus titration in eggs. Values represent means ± SD from three independent experiments. (**p < 0.01, ***p < 0.001).