Evaluation of unintended 1/96 infectious bronchitis vaccine transmission in broilers after direct contact with vaccinated ones

Infectious bronchitis virus is characterised by an extreme degree of variability which deeply affects the first-choice control strategies against the disease. Each country tends to adopt its own protocols and even vaccine producers themselves can also adopt different strategies in attempts to confront local epidemiological concerns. In the present study, we tested the potential environmental persistence, transmission ability and replication capability of a non-directly administrated vaccine strain at a hatchery and during transportation. To this purpose, we examined a single hatchery, where combined vaccination (Mass-like plus 793B-like strains) is commonly administered following the protectotype concept, whereas a single broiler flock receives only the Mass priming. Two groups of solely Mass-primed chicks were kept in contact with chicks vaccinated with both strains, during hatchery procedures and transportation, respectively. A regularly vaccinated control group was selected and all three were monitored by swab sampling until 11 days of age. Vaccine titres were quantified using vaccine-specific real-time RT-PCRs to check the kinetics of both strains. Mass titres were consistent among the groups, while the absence of the 1/96 vaccine strain in unvaccinated chicks confirmed the low risk of unintended vaccine transmission, which could complicate the diagnostic process and the epidemiological scenario.