Assessment of the Immunogenicity and Safety of an Inactivated Associated Vaccine Against Influenza and Newcastle Disease

Background/Objectives: Combined vaccination against avian influenza (A/H5N3, A/H7N7) and Newcastle disease is of practical interest for reducing handling during immunization and for achieving timely protection in poultry. The aim of this study was to evaluate an inactivated combined (associated) vaccine containing antigenic variants of avian influenza viruses A/H5N3 and A/H7N7 and Newcastle disease virus (NDV). The vaccine is protected by Patent No. 87417. Methods: Viruses with initial reproductive titers of 107.5 EID50/mL were inactivated with formaldehyde and formulated as mono-, bi-, or trivalent combinations. Antigens were adsorbed onto aluminum hydroxide gel (1.5%). Immunogenicity was assessed in chicks naïve to avian influenza and Newcastle disease using hemagglutination inhibition (HI) antibody kinetics. Vaccination was performed twice with a 21-day interval. Group administration via drinking water (5 mL/bird) was compared with parenteral administration (1.0 mL/bird). Protective efficacy was evaluated by challenge with virulent viruses at day 30. Sterility and safety/reactogenicity were assessed, and immunobiological performance was additionally evaluated under household farm conditions (337 chickens). Results: Following vaccination, protective immunity was observed starting from day 14. HI titers peaked by day 30 (7.6–7.8 log2 for A/H5N3 and A/H7N7; 9.2 log2 for NDV) and remained detectable through 180 days (4.3–4.7 log2 for avian influenza antigens; 5.1 log2 for NDV). Group administration via drinking water produced antibody kinetics comparable to parenteral vaccination, and vaccinated birds were resistant to challenge at day 30. The tested batches met sterility requirements and showed acceptable safety/reactogenicity in laboratory studies. Conclusions: The developed inactivated combined vaccine induced HI antibodies and protective immunity against avian influenza (A/H5N3, A/H7N7) and Newcastle disease. The formulation concept supports flexible antigen combinations and enables group administration via drinking water, which may reduce handling compared with separate vaccinations.