For the active immunisation of chickens to provide passive immunisation against necrotic enteritis to their progeny, during the laying period. To reduce mortality and the incidence and severity of lesions caused by Clostridium-perfringens-type-A-induced necrotic enteritis. Efficacy was demonstrated by challenge of chicks approximately three weeks after hatching. The onset of passive transfer of immunity: 6 weeks following completion of the vaccination procedure. The duration of passive transfer of immunity: 51 weeks following completion of the vaccination procedure.