Effect of time vaccination on immunization of broiler chicks against influenza A subtype H9 N2 virus

Abstract

The effective time of inactivated influenza A subtype H9N2 vaccines, in preventing the disease was evaluated in day-old broiler chicks (150). They were divided randomly into 3 equal groups. Group A chicks were vaccinated at the age of 2 days. The chicks of group B were vaccinated similar to the group A, but in the age of 8 days. Group C were kept as unvaccinated control group. Blood samples were collected from wing vein of 5 chicks of each groups weekly from day-old up to the end of experiment. Serum antibody titre of influenza A subtype H9N2 was determined by haemagglutination inhibition (HI) test. Half of the chicks of group A,B and C were challenged with influenza A subtype H9N2 virus at the age of 30 days. It was concluded that the level of mean HI titre in chicks vaccinated at 2 or 8 days was low. Vaccination on the 8 days of age showed better immune response and protection. The vaccination decreased the severity of clinical signs, morbidity and morality, but did not protect the birds against infection. Administration of killed avian influenza vaccine has useful effects in broiler chicks against infection in areas where disease is prevalent.