Fig. 2: Schematic of immunization via intratracheal inoculation method.

a The immunization scheme, b powder MicroSprayer Aerosolizer (Huironghe Company, Beijing, China), and c liquid MicroSprayer Aerosolizer (Huironghe Company, Beijing, China) used for i.t. inoculation. d Representative image of non-invasive i.t. powder inoculation. Anesthetized mice were placed on a slanted board. The trachea was exposed using a laryngoscope, the MicroSprayer Aerosolizer was inserted 25 mm from the larynx, and the powder was sprayed. BAL bronchoalveolar lavage, dppi days post primary immunization.