Disclosed are methods for preparing a vaccine against infection by infectious bronchitis virus (IBV). The methods typically include passing a heterogeneous attenuated population of IBV in chicken embryonic kidney cells, and optionally may include further passaging the heterogeneous attenuated population of IBV in embryonated chicken eggs (ECE) in order to obtain passaged attenuated population of IBV. Also disclosed are passaged attenuated populations of IBV in which the populations display a desired degree of homogeneity. Also disclosed are vaccines comprising the passaged attenuated populations of IBV and methods of vaccination comprising administering the disclosed vaccines.
