Highly pathogenic avian influenza (HPAI) H5N8 viruses of clade 2.3.4.4b continue to cause devastating outbreaks worldwide, necessitating effective vaccination strategies. The comparative efficacy of wild-type versus reverse genetics (RG)-based vaccine platforms against emerging H5Nx variants remains poorly characterized, particularly regarding cross-protective immunity mechanisms. We conducted a comprehensive comparative analysis of wild-type and RG-based H5N8 (clade 2.3.4.4b) oil-adjuvanted vaccines in specific-pathogen-free chickens (n?=?150, power analysis based on detecting two-fold titre differences with 80% power, α?=?0.05). Following single-dose vaccination, we assessed humoral and cellular immune responses, protection against homologous H5N8 (clade 2.3.4.4b), antigenically drifted and heterologous challenges [H5N1 clade 2.3.4.4b and H5N1 clade 2.2.1.2], and viral shedding dynamics using standardized assays. Both vaccines induced robust homologous antibody responses (HI titres: wild-type 7.2 ± 0.15 vs. RG 6.8 ± 0.13 log2, P?3.0 log10 reduction in respiratory tissues, with strong correlation between HI titres and protection (r?=?0.89, P?