Poulvac AE Contra-indications, warnings, etc Do not vaccinate sick, debilitated or stressed birds. Do not vaccinate birds of less than 10 weeks of age. In order to prevent spread of vaccine from vaccinated flocks to non-vaccinated flocks, all non-vaccinated birds present on the farm must be vaccinated at the same time. Vaccinated animals should not be in contact with non vaccinated animals for 42 days post-vaccination. The vaccine may induce typical signs of avian encephalomyelitis when administered orally to very young birds (less than 1 week of age).