Author
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Swayne, David |
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Kapczynski, Darrell |
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Submitted to: Book Chapter
Publication Type: Book / Chapter Publication Acceptance Date: 6/26/2007 Publication Date: 3/1/2008 Citation: Swayne, D.E., Kapczynski, D.R. 2008. Vaccines, vaccination and immunology for avian influenza viruses in poultry. In: Swayne, D.E. editor. Avian Influenza. Ames, Iowa: Blackwell Publishing. p. 407-451. Interpretive Summary: Technical Abstract: AI vaccines provide protection to birds, principally through mucosal and systemic humoral immunity against the HA protein and protection is HA subtype specific. Protection can be directly assessed by prevention of clinical signs and death, a decrease in number of birds infected, reduction in the quantity of challenge virus shed from respiratory and alimentary tracts, and prevention of contact transmission in in vivo experimental studies. Protection can also be assessed indirectly through measurement of protective antibody levels in vaccinated birds or assaying the quantity of HA protein in the vaccine. AI vaccines should be sufficiently potent to protect birds under a variety of field conditions. AI vaccines are based on four technology platforms: 1) inactivated whole AI virus vaccines; 2) in vitro expressed HA protein; 3) in vivo expressed HA protein in vectored systems; and 4) HA-based DNA vaccine. However, only inactivated AI virus, rFP-AIV-H5 and rND-AIV-H5 vaccines are currently licensed and used in the field in various countries. Historically, inactivated AI virus vaccines have used seed virus strains predominately based on LPAI, and occasionally, HPAI outbreak viruses. Such seed strains have been broadly protective within an HA subtype and requiring less frequent change of seed strains than has been necessary for human influenza A vaccines. In the past five years, some seed strains have been produced by reverse genetics utilizing the HA and NA genes from an outbreak virus and the six internal genes of a high growth producing influenza A vaccine virus strain. AI vaccines have been used in emergency, routine or preventative vaccination programs. Several issues are important for field use of AI vaccines: 1) AI vaccine use should be part of a comprehensive total AI control program; 2) the vaccine strain must be of the same HA subtype and should be protective in the target species based on in vivo studies against a recent circulating field virus; 3) the vaccine should have sufficient HA content (inactivated or in vitro expressed HA system vaccine with minimum titer of 1-5 ug HA/dose) or adequate live virus titer (vectored vaccines) sufficient to produce a protective immune response, or serological evidence that administration will produce sufficient HI titer to protect birds; 4) inactivated or in vitro expressed HA system vaccines should be emulsified within a good oil adjuvant system; 5) manufacturing of AI vaccines must be standardized in order to produce consistent and efficacious vaccine batches; 6) procedures must be established for proper storage, distribution, and administration of the vaccine; 7) establishment of biosecurity practices to prevent vaccination crews or other service personnel from accidental spreading of field virus; 8) proper serological or virological surveillance systems must be in place to determine if vaccination has produced protective immunity and to monitor vaccinated populations for possible field virus circulation (i.e. DIVA); and 9) an exit strategy from emergency vaccine use should be developed to prevent vaccination from becoming a routine program with associated AI virus endemicity. AI vaccines must be periodically re-evaluated to determine if they are still effective against circulating field virus strains and if no longer protective, vaccine strains should be replaced. Requirements for licensing AI vaccines will vary with each country depending on specific requirements of the national veterinary biologics authority in areas of safety, purity, potency, and label approval for species, and age and route of administration. |
