INTRODUCTION 1.2 How Do Vaccines Work? Poultry vaccines are biological products that induce an immune response to specific disease causing agents. Depending on the vaccine, they can be administered in various ways which are discussed in this guide. Depending on the type of antigen in the vaccine, the bird’s immune system will react, creating a “memory” response of antibodies and immune cells. The more a bird is exposed to the same antigen, typically the greater the antibody response and resulting protection. For this reason, many flocks are vaccinated multiple times for the same disease. 1.3 Vaccines and Vaccination Vaccines for poultry come in three general forms:
Modified or Attenuated (Live), Inactivated (Killed), and Recombinants. Live vaccines are strains that are naturally or genetically modified milder forms of field strains. Inactivated vaccines are whole viruses or bacteria that have been killed during production and formulated into a deliverable product. Recombinant vaccines, known also as vector vaccines, are made by using live viruses or bacteria as a vector to transport the gene coding for the protective antigen of a second infectious agent for which immunity is desired. COBB VACCINATION MANAGEMENT GUIDE Vaccine Vectors Examples of recombinant vaccines include:
The main viral vectors used for the development of recombinant vaccines are Herpes Virus of Turkey (HVT) and the Poxvirus. These viruses have genomes that are large enough to accept large inserts. » HVT expressing Newcastle Disease virus protein » HVT expressing Avian Laryngotracheitis virus protein » HVT expressing Infectious Bursal Disease virus protein Recent research has shown differences in replication within the recombinant HVT (rHVT) products, and therefore, it is very critical to add the Rispens vaccine strain when long-life birds such as breeders and commercial layers are vaccinated with rHVT products.
» HVT expressing two inserts (Infectious Bursal Disease and Newcastle Disease) » Fowl pox virus expressing Avian Influenza virus protein » Fowl pox virus expressing Newcastle Disease virus protein There is also a clear interference between rHVT vaccines and conventional HVT strains. Therefore, no chick should receive both products as the interference will lead to poor vaccine replication and may affect the expression of the insert. » Fowl pox virus expressing Infectious Laryngotracheitis virus protein 3