Vaccination of chickens with newcastle disease and infectious bronchitis vaccines administered singly and in combination.

The reactivity and immune response were determined in chickens following the administration of Newcastle disease (ND) and infectious bronchitis (IB) vaccines given singly and in combination. When given singly, the IB component resulted in an earlier appearance of respiratory signs than when it was combined with ND vaccine. The intensity of the respiratory reaction appeared similar in each case, however. Measured by virus-serum neutralization and from challenge with ND and IB viruses, no evidence of interference in the inducement of immunity was present with either vaccine fraction. The possible effect of vaccine titers and strain characteristics was discussed briefly.