Onset of immunity following in ovo delivery of avian metapneumovirus vaccines

Avian metapneumovirus (aMPV) is an important cause of disease in chickens and turkeys. As infection can occur early in life and spread of the virus throughout a flock is rapid, an early onset of immunity post-vaccination would be advantageous. We have studied the serological immune response and the onset of protective immunity of an aMPV vaccine delivered to chickens via the in ovo route compared to oculonasal delivery at day old. A 1000-fold lower dose delivered in ovo to chicken specific pathogen free (SPF) embryos, than vaccination at day old, provided a significantly higher antibody response. In the presence of maternally derived antibody (MDA), there was no significant difference in antibody response between the vaccination routes. However, the onset of immunity (OOI) for the vaccine delivered to MDA positive chicken embryos was 5 days post-hatch in comparison to 8 days post-hatch for the same dose of vaccine given at day old indicating that chicks would be protected against disease earlier in the field if vaccinated by the in ovo route. In further experiments the OOI for a turkey vaccine delivered to MDA positive turkey embryos was shown to be 8 days post-hatch.