Comparison of the efficacy of bivalent inactivated vaccine (H5-Re13 and H5-Re14 strains) with inactivated H5N2 vaccine in commercial broiler chickens against currently circulating highly pathogenic avian influenza H5N1 clade 2.3.4.4b virus

Avian influenza, particularly the highly pathogenic H5N1 virus, continues to pose a persistent threat to poultry populations worldwide. In Egypt, the outbreaks of H5N1 have a significant economic and public health impacts. To deal with this ongoing issue, vaccination remains a cornerstone strategy in mitigating the impact of avian influenza in broiler chicken populations.This study aims to evaluate selected commercially inactivated H5 vaccines in broiler chickens in Egypt, focusing on their effectiveness against the currently circulating highly pathogenic H5N1 strain clade 2.3.4.4b. Inactivated reassortant avian influenza virus vaccine (Re-13 & Re-14 strains) and inactivated avian influenza H5N2 vaccine, represented by Gp1 and Gp2 respectively, were studied and by assessing their protective efficacy and immunological responses elicited by these vaccines. The mean HI titers (log2±SD) against the heterologous inactivated HPAI H5N1 antigen at 31 day old (DO) was 6.6 ± 0.52 and 3 ± 0.53 with mean shedding reduction 4 and 1.5 (log10) for Gp1 and Gp2, respectively. Moreover, the protection percentage after challenge infection with HPAI H5N1 clade 2.3.4.4b was 100% and 55 % for Gp1 and Gp2, respectively. Our results indicate that the reassortant avian influenza virus vaccine (Re 13 & Re 14 strains) was effective because the seed viruses in this vaccine are genetically close to the H5N1 virus clade 2.3.4.4b currently circulating in Egypt.