Immunogenicity and Protective Efficacy of a Serum-Free Suspension MDCK Cell Culture-Based Inactivated H3N8 Avian Influenza Vaccine Compared with an Egg-Based Counterpart in Chickens

H3N8 subtype avian influenza virus (AIV) circulates in poultry with occasional zoonotic potential and vaccines are crucial for preventing and controlling avian influenza.Here, two inactivated vaccines were prepared against the H3N8 AIV with GD1102 as vaccine strain: an embryonated chicken egg-based vaccine (E-vac) and a serum-free suspension MDCK cell-based vaccine (C-vac).The efficacy of both vaccines was evaluated in specific pathogen-free chickens.All vaccinated groups and the challenge control were intranasally challenged with 10 6 EID50 of GD1102 at 14 days post-vaccination (dpv) while the negative control group received no challenge.HI antibody titers, viral shedding, tissue viral loads, and pathological lesions were systematically assessed.Both vaccines elicited robust humoral immune responses at 7 dpv and the C-vac group had significantly higher HI titers than the E-vac group (p<0.01).However, at 14 dpv, both groups showed similar titers (HI>6 log2).Compared with the control group, both vaccines effectively reduced viral shedding and lessened histopathological lesions.These findings suggest that C-vac elicits a rapid antibody response and confers effective protection.Therefore, C-vac can be considered a promising new platform for H3N8 avian influenza vaccines.