2.3 Immunization and challenge

Female BALB/c mice (6-8 weeks old) were randomized into groups. Six groups were subcutaneously immunized with 26.6 µg (100 µL) candidate vaccines, respectively. The Cap VLPs group (20 µg, Cap molar equivalent) is serves as positive control. The Carbopol 971P as adjuvant (Ding et al., 2017). Booster immunization was performed at the 21 and 42 days post initial immunization (dpi). Serum samples were collected at 63 dpi and stored at -20 °C until use. Mice in each group were divided into three groups (n=9). Mice were lightly anesthetized and intranasally challenged with lethal dose humans, swine and avian IAV at 64 dpi, respectively. Survival rates and body weight loss were monitored daily for 14 days post challenge (dpc). Mice were humanely euthanized if weight loss of ≥ 25%.