Trivalent fowl adenovirus vaccine (serotype-4/8b/11) provides efficient protection with long duration of immunity

Fowl adenovirus (FAdV) is a significant viral pathogen with major economic impact on the global poultry industry. Recent epidemiological studies indicate that predominant strains in Asia, including Korea, are FAdV-4 (species C), 8b (species E), and 11 (species D).

This study evaluated a novel trivalent inactivated FAdV vaccine containing antigens from FAdV-4, 8b, and 11.

An SD1356-like FAdV-8b strain, representing newly emerging variants in Asia and the Middle East, was included as an immunogen. Prior to vaccination-challenge trials, pathogenicity of FAdV-4, 8b, and 11 was assessed in chickens via oral, intramuscular, and intravenous routes. These models were used to determine the minimum protective dose. Cross-neutralization assays were performed using sera from monovalent vaccinations for each serotype. Duration of immunity was evaluated in specific pathogen-free chickens following a single vaccine dose.

Intravenous challenge produced the highest mortality across all serotypes, including the relatively low-pathogenic FAdV-11. A vaccine dose of 10^7.0 TCID₅₀/bird induced strong neutralizing antibody responses and provided complete protection against virulent strains. Sera showed no cross-neutralization between heterologous serotypes, emphasizing the necessity of multivalent formulations. Protective antibody titers were maintained up to 78 weeks of age.

The trivalent vaccine provides effective protection against predominant FAdV-4, 8b, and 11 strains. These findings support the use of multivalent vaccines to achieve broad and sustained immunity against emerging FAdV infections in poultry.