The combination of Massachusetts type vaccine viruses with QX or 4/91 vaccine variants induce protection against a challenge with QX or 793B type field viruses

Many different genotypes of infectious bronchitis virus circulate in Europe in chickens and turkeys. A common control strategy to prevent the consequences of infection is vaccination with live attenuated vaccines. With it, protection against the homologous strains used and cross-protection against virulent heterologous strains are sought as an additional value. In this work, two typical Massachusetts+variant vaccine combinations were evaluated as valid to develop protection against the challenge of virulent strains frequently circulating in the field.

Vaccination plans with combinations of different infectious bronchitis (IB) vaccine virus serotypes may protect against challenge with field viruses for which there are no homologous vaccine viruses. Live attenuated H120 vaccines are safe and efficacious against Massachusetts-type viruses and provide strong protection against homologous challenge and variable protection against heterologous challenge. Live attenuated vaccines have been developed with variant strains that protect against challenges with homologous strains and offer some degree of cross-protection against other heterologous strains.

Combining live attenuated IB vaccines on the day of birth makes it possible to stimulate and amplify actively acquired immunity against field strains homologous and heterologous to those of the applied vaccines. Vaccination on the first day of life in the hatchery is more cost-effective compared to programs that are applied during the first weeks of life.

In the present study, cross-protection against challenge with a type 793B strain after vaccination with a combination of the H120 and type QX strains was evaluated. A QX-like field virus challenge was also included. In addition, the efficacy of a combination of IBV vaccine strains Ma5 and 4/91 against challenge with these same viruses was tested. At the time of challenge, samples were taken to determine antibody titers against IB virus. Five days later, ciliostasis was evaluated as a measure of efficacy.

J. Boelm + JJ de Wit, “The combination of Massachusetts type vaccine viruses with QX or 4/91 vaccine variants induce protection against a challenge with QX or 793B type field viruses.” J Avium No. 3, September 2022.

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