Broilers: Vaccination at day old by coarse spray or eye drop route. Layers and Breeders: Vaccination at day old by coarse spray or eye drop route. Revaccination: At approximately 6 weeks of age by coarse spray or the eye drop methods. Immunity and Vaccination Reaction The duration and intensity of the vaccination reaction 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. After a first vaccination an adequate immunity against Massachusetts type of IB will last for approximately 6 weeks, provided that the vaccine is properly administered. Emergency vaccination during the laying period may be accompanied by a transient drop in egg production.