Fig. 1

Strategy for the animal experiment. Mice were randomly divided into four groups and orally vaccinated with initial immunization (day 1–3), booster immunization (day 11–13), and final immunization (day 21–23). Samples were collected on days 0, 14, 28, and 42 for ELISA and RT-qPCR analysis. Histology and virus titers were assessed using lung samples taken 7 d following viral challenge