For use in chickens, 18 day-old embryonated broiler hatching eggs.

For the active immunisation of chickens to prevent mortality, clinical disease and weight loss, and to reduce the acute lesions of bursa of Fabricius associated with infection with both classical and very virulent avian Infectious Bursal Disease (IBD) viruses.

The release of the vaccine virus from the complex (and therefore immunisation) is influenced by the natural decline of maternally derived antibodies (MDA), which has been found not to occur until MDA has reached relatively low levels. The onset of clinical protection is achieved within 1 day after the first signs of vaccine virus effect in the bursa of Fabricius. This is expected to occur between 3-4 weeks of age in broiler flocks hatching from eggs of layers immunised against IBD using the customary immunisation programs. Duration of immunity is at least 42 days.

The virulent challenge tests conducted to support the claim were carried out on broilers having an MDA ELISA titre of 6,000 (1 day old chick).

Field trials carried out showed that vaccine virus replication in the bursa of Fabricius occurs in broilers having at hatch MDA titre levels of up to 14,000 ELISA units, but the protection of these birds was evaluated only based on serological data and histology of the bursa of Fabricius.