Infectious bronchitis virus (IBV) variants constantly emerge and causes significant economic losses by affecting both vaccinated and unvaccinated chickens.  This study, conducted in 2022-2023, investigated frequent outbreaks of Infectious Bronchitis Virus (IBV) in broiler and layer chicken flocks in Ismailia Governorate, Egypt, despite widespread vaccination. Samples were collected from 10 farms, each employing a vaccination regime of H120 (live attenuated vaccine) on the first day, followed by 4/91 vaccination after a week. Despite vaccination, clinical signs of IBV appeared after 25 days, with mortality rates of 20-30% and morbidity rates of 40%. Pooled trachea, lung, and kidney samples from the flocks underwent Reverse Transcription-Polymerase Chain Reaction (RT-PCR) analysis, focusing on a 457bp fragment within the hypervariable region of IBV. Out of 10 farm, two samples were positives for IBV. Nucleotide and amino acid sequence analyses were conducted on one of the positive samples. Phylogenetic analysis identified our isolates as belonging to the Genotype I clade 23 (GI-23), clustering with the VAR II strain previously isolated in Egypt, showing an 84% identity to S1 gene sequences with GenBank accessions MH021175 and KU79007. Histopathological examinations revealed significant changes in the infected birds. Tracheal samples displayed hyperplasia and degenerative changes in the epithelium, accompanied by edema. Lung tissues exhibited pneumonia, bronchitis, bronchiolitis, perivascular edema, and leukocyte infiltration. Kidney samples showed lymphocytic aggregation in the cortex and medulla, epithelial degeneration, and hemorrhage. These findings underscore the persistent challenge of IBV in poultry, even in vaccinated flocks, and the need for ongoing surveillance and vaccine development.