Clinical encephalitis following avian encephalomyelitis vaccination in broiler breeder pullets

Twelve-to-fourteen-week-old broiler breeder pullets and cockerels from two different companies were found to have encephalitis 2 weeks after vaccination with avian encephalomyelitis (AE) vaccine. Histologic examination and virus isolation indicated that affected chickens had AE. All chickens had been vaccinated with either one of two serials of AE vaccine approximately 2 weeks before the onset of clinical signs.