Heterologous prime-boost vaccination programs against Newcastle disease virus genotype VII in chickens.

The effectiveness of two vectored ND vaccines (Innovax® ND and Vectormune® ND) was tested, in single and prime-boost vaccination programs, against challenge with velogenic NDV genotype VII, in eight chicken groups (G). G1 and G2 were control groups. G3-5 received Innovax® ND, while G6-8 received Vectormune® ND on the hatchery. Additionally, G4 and G7 received live La Sota two-weeks later, and G5 and G8 received inactivated vaccine one-week later. On the challenge day, G3 (Innovax® ND vaccine alone) had lower HI titer than G6 (Vectormune® ND vaccine alone) (p < 0.05). Boosting with inactivated vaccine instead of La Sota increased serological response. G3 had the same HI titer as G2 (positive control) but decreased viral shedding significantly after the 3rd day post challenge (d pc). G8 (Vectormune® ND plus inactivated vaccine) had 86.5 % decrease of viral shedding on the 3rd d pc, while that of G7 (Vectormune® ND plus La Sota) persisted until the 6th d pc. All regimens increased weight gain (p < 0.05), fully protected against mortality, and showed few clinical signs. Prime-boost vaccines provided significant reduction and time shortening of heterologous viral shedding.