The inactivated infectious bronchitis virus (IBV) vaccine used as booster in layer hens influences the breadth of protection against challenge with IBV variants.

To achieve long term protection of laying and breeding hens against aberrant egg production caused by infectious bronchitis virus (IBV), a vaccination programme incorporating both live-attenuated and inactivated IBV vaccines is required. High quality IBV vaccines of both types are widely available, but the number of IBV variants of global importance continues to increase and it is not possible to develop vaccines against each one of them. Therefore, it is desirable to perform studies under controlled conditions to determine which IBV vaccine(s) provide the best protection for laying hens against different IBV challenges. Previous vaccination and challenge studies have shown that it is possible to obtain relevant data in a small number of laying hens housed under conditions of strict isolation. The present work extends this finding by investigating the efficacy, against challenge with five IBV strains of global importance, of an IBV vaccination programme including two live-attenuated IBV vaccines (Massachusetts and 793B types) and three different commercially available inactivated vaccines each containing antigen against at least one IBV strain. The results reported here confirm the importance of IBV vaccination for laying hens, show that efficient live priming makes a beneficial contribution to this protection and confirm that inactivated IBV vaccines contribute significantly to effective protection against at least the five IBV challenge strains used here. Furthermore, we provide data to support the "protectotype concept", long-established using different live-attenuated IBV vaccines in young chickens, is valid in broadening protection against IBV challenges in laying birds.RESEARCH HIGHLIGHTSIBV vaccination is essential as an aid in protecting laying hens against IBV infection.Live priming is a beneficial part of the IBV vaccination programme.IBV inactivated vaccine improves IBV protection.Heterologous IBV protection is confirmed in laying hens.

Effect of IBV D1466 on egg production and egg quality and the effect of heterologous priming to increase the efficacy of an inactivated IBV vaccine.

To protect layers, breeders and grandparents against damage by infectious bronchitis virus infections during the laying period, vaccination using live priming followed by a boost with inactivated IB vaccine is commonly used. For many IB variants, homologous live vaccines are not available for priming. Very little is known about the efficacy of priming with heterologous live IB vaccines (or combination of live IB vaccines) to induce broad IB protection in long-living chickens. In this study, the protection levels induced by vaccination programmes with only heterologous live priming by a Massachusetts vaccine and a 4/91 vaccine, only a multivalent inactivated vaccine that contained D1466 antigen and a combination of both, against a D1466 challenge were compared. The infection with infectious bronchitis virus D1466, a genotype II, lineage 1 virus, was able to cause serious damage to the unvaccinated laying hens resulting in respiratory signs, a long-lasting drop in egg production and loss of egg quality. All three vaccination programmes induced significant levels of protection against challenge with a pathogenic D1466 strain. Overall, the vaccination programme using the broad heterologous live priming and the inactivated vaccine provided high protection against the combination of egg drop and loss of egg quality. The results showed that this combination of heterologous live vaccines was able to increase the efficacy of the inactivated infectious bronchitis virus vaccine despite the very low antigenic relationship of both live vaccines with the challenge strain.