The duration and intensity of the vaccination reaction (sneezing) and the establishment of a solid immunity are generally dependent on the health and condition of the chickens. Hygiene and management are also important in the post-vaccination period. An adequate immunity against ND and the Massachusetts type of IB will last for approximately 6 weeks, provided that the vaccine is administered correctly. In areas where ND is endemic, a second vaccination with Clone 30 should be given at an age of approximately 4 weeks. Emergency vaccination during the laying period may be accompanied by a transient drop in egg production.