Laboratory safety and immunogenicity evaluation of live attenuated avian infectious bronchitis GI-23 virus vaccine

Avian infectious bronchitis virus (IBV) is responsible for a highly contagious disease that poses a significant threat to the poultry industry due to its high rates of evolution. The occurrence of vaccination failure can frequently be attributed to the emergence of novel strains that exhibit antigenic divergence from conventional vaccine strains. This study aims to evaluate the safety and efficacy of the Eg/1212B-based live attenuated virus vaccine indicated for immunization of chickens against nephropathogenic GI-23 variant strains reported globally. Studies were designed in compliance with European Pharmacopeia Ph. Eur. 0442. The attenuated vaccine virus did not exhibit any tendency to revert or increase in virulence after five back-passages in SPF chickens. Ciliostasis scores and kidney lesions (histology) were comparable between vaccinated and control birds. No chicken showed clinical signs of an infection with IBV or died from causes attributable to the vaccine after receiving a 10× overdose. A single vaccination was able to protect the birds in a challenge model with a recent European wild-type IBV strain. The study demonstrated an onset of immunity of 21 days and a duration of immunity lasting up to 56 days. Vaccination administered individually through the ocular route resulted in a protection rate of 100 % to 85 %, whereas mass application by spraying offered a protection rate of 85 % to 80 %. In conclusion, the safety and efficacy data confirm a positive benefit/risk balance, and the investigated product can be considered a suitable vaccine candidate for controlling avian infectious bronchitis nephropathogenic variant strains related to GI-23.