Onset of Immunity
In chickens free of maternally derived antibodies (MDAMaternally Derived Antibodies: antibodies produced by the breeders and transmitted to their progeny through the egg yolk.) against Avian Influenza virus (AIVAvian Influenza Virus), early protection comes exclusively from the active immunity induced by the vaccine replication. According to controlled studies, 2 weeks are necessary to reach protection ( #8 , #9 ), although earlier resistance to challenge has not been tested yet.
In chickens with MDA against AIV, protection comes also from MDA which are actually protective ( #9 ), and it has been observed that active immunity induced by vaccination works together with MDA protection to increase overall early protection. For this reason, in countries where AIAvian Influenza is endemic, vaccination of breeders against AI complements and does not detract from day-old vaccination of broilers and pullets.