Duration of Immunity (DOI)
Data regarding efficacy of the vector rHVT-HA5 to protect long living chickens against very late challenge are not available yet. However, the following facts point to signs of long-lasting protection:
- HVTHerpes Virus of Turkey is known to persist indefinitely in vaccinated animals, so that expression of the HAHemagglutinin insert inside the vector rHVT-HA5 vaccine is likely to persist as well as corresponding induced protection.
- The HI test ABAntibody / Antibodies response (homologous antigen) to the vector rHVT-HA5 vaccination up to 12 weeks of age in commercial layer pullets with or without MDAMaternally Derived Antibodies: antibodies produced by the breeders and transmitted to their progeny through the egg yolk. against H5N1 revealed titers increasing and then remaining steady.
- Layer pullets of 2 different breeds, vaccinated at the hatchery and reared under the heavy diseases challenge conditions of Egypt, were transferred at 19 weeks of age to BSL3 facilities for virulent challenge. Protection levels of 73% and 60% were recorded, despite the presence of disease problems unrelated to AIAvian Influenza. ( #15 ).