A Matching Multivalent Vaccine Candidate Combining Velogenic NDV Genotype VII and Variant IBV Protects Chicken from Virulent Challenge and Eliminates Virus Shedding

Vaccination is the main preventive measure against infectious bronchitis virus (IBV) and Newcastle Disease virus (NDV) infections. Vaccination can partially protect against IBV because of the continuous emergence of variant strains. The aim of the current study is to evaluate the efficacy of multivalent inactivated vaccine candidate combining two IBV lineages (M41; GI-lineage) and (VarII; GI-23 lineage) along with NDV (genotype VII) using Montanide ISA-71 oil adjuvant against circulating variant IBV and velogenic NDV field strains. Our results revealed that the prepared vaccine candidate was sterile, safe, and potent due to its ability to stimulate the production of specific antibodies against IBV and NDV starting from 1-week post vaccination (WPV). The maximum levels of specific IBV ELISA antibody titers (2926) were observed at the sixth week post vaccination. HI antibodies against IBV reached its peak 5th WPV (9.2 log2) while HI antibodies against NDV reached its peak 4 WPV (9.5 log2). Vaccinated chickens showed 100% protection against challenge with virulent NDV, and variant IBV with complete absence of clinical signs and postmortem lesions compared to challenged non vaccinated groups. Our results revealed that the prepared vaccine candidate in this study is able to elicit good immune response, eliminate viral shedding, and provide complete protection against virulent challenge. Meanwhile, it is better to control both IBV and NDV outbreaks in a single shot consequently that will save time, effort and reduce stress during chicken vaccination.