الفهرس 
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Abstract
In the present study the efficacy and safety of three inactivated Avian Influenza (AI) vaccines; monovalent heterologous AI vaccine (H5N2), monovalent homologous AI vaccine (H5N1) and combined AI(H5N2) and Newcastle Disease vaccine (ND) were tested for sterility, infectivity and immunogenicity according to the Office des epizootic international OIE-Manual, (2004). Immunogenicity and duration of immunity in commercial broilers were tested and compared with SPF chicks by vaccination of chicks at 7 day of age for evaluation of the onset, level and duration of immunity by HI for 5 weeks post vaccination at weekly intervals by HI test using three antigens; Chinese H5N1, Mexico H5N2 and Egyptian H5N1.Sentinel birds were reared with vaccinated groups to ensure that there is no introduction of infection to the experimental groups. Samples were collected from different birds and sentinel birds and examined for the presence of AI genome by Real time-RT-PCR (RRT PCR) test. The findings indicated that SPF chicks vaccinated at 7 days of age responded best to vaccine, and elicited the highest post vaccination antibodies as compared with commercial broilers chicks vaccinated at 7 days of age which could be attributed to interference of maternal antibodies. In this study the results revealed significant differences between three antigens used in HI test so it’s highly recommended to use homologous HI antigen in HI test for estimation of avian influenza antibodies to accurately evaluate the flock immune status and potency of vaccine used but to monitoring the efficacy of the vaccine to optimal protection against field strain we should used the field strain antigen in HI test.