Background/Objectives: Biosecurity and stamping out are key control measures against H5 high pathogenicity avian influenza (HPAI) outbreaks. Vaccination in poultry is an additional tool to reduce disease risk and facilitate timely containment. This study aimed to establish a candidate vaccine strain against H5 HPAI in Asia and validate its protective efficacy. Methods: Based on genetic and antigenic analyses, a representative HPAI virus, A/duck/Vietnam/HU16-DD3/2023 (H5N1), collected in northern Vietnam, was selected to generate a candidate vaccine strain, rgPR8/VN23HA∆KRRK-NA (rgPR8/VN23; H5N1), using reverse genetics, followed by formulation of an inactivated oil-adjuvanted vaccine. Vaccine efficacy was evaluated by measuring humoral antibody responses after intramuscular vaccination and by assessing mortality and virus recovery following intranasal challenge with a clade 2.3.4.4b virus, A/Ezo red fox/Hokkaido/1/2022 (H5N1). Results were compared with those obtained using an antigenically homologous vaccine to the challenge strain and a Japanese stockpiled vaccine. Results: All vaccinated juvenile chickens developed sufficient immunity to survive the challenge at 21 days post-vaccination. The rgPR8/VN23 (H5N1) and homologous vaccines markedly reduced virus recovery, suggesting near-sterile protection, whereas low-titer viruses were transiently detected in chickens vaccinated with the stockpiled vaccine. The rgPR8/VN23 (H5N1) vaccine conferred clinical protection in juvenile chickens as early as 8 days post-vaccination. A single dose of the rgPR8/VN23 (H5N1) vaccine provided incomplete protection in laying hens, whereas a double-volume regimen improved protective efficacy. Conclusions: The rgPR8/VN23 (H5N1) vaccine conferred strong immunity to juvenile chickens; however, a refined vaccination strategy may be required to achieve complete protection in laying hens.

Although biosecurity and stamping out are key control measures, vaccination in poultry is an additional tool against H5 high pathogenicity avian influenza (HPAI) outbreaks to reduce disease risk and facilitate timely containment. This study aims to establish a candidate vaccine strain against H5 HPAI in Asia and validate its protective efficacy. Based on genetic and antigenic analyses, A/duck/Vietnam/HU16-DD3/2023 (H5N1), collected in northern Vietnam, was selected for establishing the vaccine candidate strain. The vaccine strain, rgPR8/VN23HA∆KRRK-NA (H5N1; rgPR8/VN23), was generated. Inactivated oil-adjuvanted vaccines were prepared from rgPR8/VN23 (H5N1), NIID-002 (H5N1), which originated from HPAI virus, A/Ezo red fox/Hokkaido/1/2022 (H5N1; Fox/Hok/1/22), and a Japanese stockpiled vaccine strain with a distinct antigen. These vaccines were intramuscularly injected into juvenile chickens or adult laying hens. All vaccinated juvenile chickens acquired optimal immunity and survived for 14 days after intranasal challenge with Fox/Hok/1/22 at 21 days post-vaccination (dpv). The rgPR8/VN23 and NIID-002 vaccines markedly reduced virus shedding, suggesting near-sterile protection. However, low-titer viruses were transiently detected in chickens vaccinated with the stockpiled vaccine strain. The rgPR8/VN23 vaccine induced immunity in juvenile chickens against Fox/Hok/1/22 as early as 8 dpv. Intriguingly, a single dose of vaccine was insufficient to provide protective immunity to laying hens. Protective efficacy increased with a double-volume dose vaccine. These data confirm that the antigenicity-matched vaccine conferred sterilized immunity in 21 days and clinical protection in 8 days to juvenile chickens, although complete protection of hens may require a refined vaccination strategy.

This study investigated the association between growth traits in goats and polymorphisms in the POU1F1 (AluI and PstI) and GH1 (HaeIII) genes using both single-marker and haplotype-based approaches. A total of 79 goats were genotyped, and growth performance was evaluated based on body weight (BW), average daily gain (ADG), and relative growth rate (RGR) across developmental stages. All loci were polymorphic; however, the POU1F1/PstI locus deviated from Hardy-Weinberg equilibrium (P=0.003). Association analyses revealed that the POU1F1/PstI locus was significantly associated with ADG and RGR in a stage-dependent manner, including ADG3-6 (P=0.024), ADG3-10 (P=0.023), and RGR0-3 (P=0.003). In contrast, the POU1F1/AluI locus showed limited and stage-dependent effects, with significant associations confined to later stages, particularly for body weight at 6 and 10 months and cumulative post-weaning gain (P0.05). Additive and dominance models further supported the contribution of the POU1F1/PstI locus to growth rate variation. In addition, four haplotypes were identified with T-T being the most frequent (71.2%) and tending to show more favorable post-weaning growth performance. Overall, POU1F1, particularly the PstI polymorphism and linked haplotypes, showed stronger associations with goat growth traits than GH1. Because the population was small and some genotype classes were unbalanced, these results remain preliminary and require validation in larger, diverse populations before practical use in selection programs.