Infectious bronchitis virus (IBV) has a variety of serotypes that cause many problems in the poultry industry. Two H120 and H120-D274 live vaccines were evaluated against strain IS/1494/06 (variant 2) IBV challenge. The study aimed to determine whether it was possible to achieve success in controlling disease symptoms and pathological lesions and reducing virus shedding by combining two types of vaccines against different severities of poultry IBV. After random selection of 100 specific pathogen-free chickens, four 25 chicks/group experimental groups were arranged in the H120 (IB-H120, Intervet��; Serial No: **** at 1st day + Booster 14th day + Challenged with IS/1494/06- 14 DPV), H120-D274 (Poulvac�� IB Primer at 1st day + Booster 14th day + Challenged with IS/1494/06- 14 DPV), Control (No vaccine + No Challenge), and Challenged (No vaccine + Challenge). After euthanasia of the animals on the 42nd day of the research, serum neutralization (days 14, 28, and 42), ELISA (14 days after the booster vaccine and before challenged), Ciliostasis (7 days after the booster vaccine and seven days after challenged), and pathological lesion scores were evaluated on day 14 after being infected with IS/1494/06 type 2 strain (day 42). Moreover, the virus shedding was monitored by real-time polymerase chain reaction. Infection with the IS/1494/06 variant 2 strain showed high to moderate Ciliostasis and pathologic scores. All groups that received the IB-H120-D274 vaccine had fewer lesions relatively. The IB-H120-D274 vaccinated groups showed the highest protection rates and high protection scores (70.3) than the IB-H120 vaccine groups (24.4). The virus shedding was significantly reduced in groups that received the H120-D274 vaccine compared to those that received the IB-H120 vaccine. In conclusion, the homologous IB-H120-D274 vaccine showed superior results compared to the IB-H120 vaccine.
