The level of antibody by ELISA,immunsosuppressive effect baes on the response of birds to Newcastle disease vaccination and damage to bursa of Fabricius by IBD vaccination were studied. The efficacy of six different IBD vaccination schedules were studied using intermediate and intermediate plus strains of vaccines either alone or in combination. In vaccinated groups, the sero-conversion of the vaccine virus was noticed during fourth week, reaching to the peak between eight to twelve weeks of age in different groups. Afterwards, there was a gradual decrease in the titres, by the end of 20th week (maximum period tested). There was no significant difference in the titres of different treatment groups. However, all the groups showed titres above protective level during the entire period of study. There was significant difference in bursa body weight (B-BW) ratios of vaccinated groups in comparison with control group. Histopathological studies of bursal sections revealed depletion of lymphoid follicles, presence of cystic spaces, edema and hemorrhages. The birds vaccinated with hot strain of IBD vaccine showed metaplastic changes, presence of foam cells with pronounced interfollicular fibrosis. The bursal scores were maximum in the groups vaccinated with hot strains of IBD vaccines.

Test vaccines comprised of inactivated water-in-oil emulsions containing various antigen levels were prepared using a non-pathogenic H5N1 avian influenza (AI) virus, A/duck/Hokkaido/Vac-1/04 (H5N1). The potencies of these test vaccines were evaluated by two experiments. In the first experiment, the triangular relationship among the antigen levels of test vaccines, the hemagglutination inhibition (HI) antibody response, and the protective effect against challenge with a highly pathogenic avian influenza (HPAI) virus, A/chicken/Yamaguchi/7/04 (H5N1), was confirmed. Then lasting immunity of chickens after a single-shot vaccination was confirmed in the second experiment. As a result, complete protection after the challenge was observed in chickens immunized by test vaccines with an antigen level of 160 HA units/dose or higher. Thus, it was ascertained that the minimum antigen level in the AI vaccine was 160 HA units/dose, and the minimum HI antibody titer that could protect chickens from HPAI virus infection-related death was considered to be 1:16. Dose-dependent HI antibody responses were observed in chickens after the vaccination. Thus, 640 HA units/dose were thought to be similar to the optimal antigen level. Alternatively, the HI antibody titers of chickens, injected with the vaccine containing 640 HA units/dose, were maintained at 1:181 or higher for 100 weeks after the single-shot vaccination.