Antibody response against IBV (A) and NDV (B) in 1-day-old SPF chicks vaccinated at day 1 and day 14 of age with different rNDV vectored IBV vaccine candidates. A The level of IBV-specific antibodies in chicken serum samples on week 5 (prior to challenge) was determined by ELISA. Mean absorbance values and SEM are shown for each group. Statistically significant differences versus the control group are indicated by asterisk. B The level of NDV-specific antibody titers in chicken serum samples on week 2 (prior to boost) and on week 5 (prior to challenge) were determined by hemagglutination inhibition (HI) assay. Mean and SEM of each group are shown.