For active immunisation of chickens against avian influenza type A, subtype H5.Reduction of clinical signs, mortality and excretion of virus after challenge with a virulent H5N1 strain, were shown by two weeks after a single dose vaccination.Serum antibodies have been shown to persist in chickens for at least 7 months and studies performed with other vaccine strains show that serum antibodies would be expected to persist in chickens for at least 12 months after administration of two doses of vaccine.