title: Variation in protection of four divergent avian influenza virus vaccine seed strains against eight clade 2.2.1 and 2.2.1.1. Egyptian H5N1 high pathogenicity variants in poultry.
abstract: BACKGROUND
  Highly pathogenic (HP) H5N1 avian influenza virus (AIV) was introduced to Egyptian poultry in 2006 and has since become enzootic. Vaccination has been utilized as a control tool combined with other control methods, but for a variety of reasons, the disease has not been eradicated. In 2007, an antigenically divergent hemagglutinin subclade, 2.2.1.1, emerged from the original clade 2.2.1 viruses.
  
  
  OBJECTIVE
  The objective was to evaluate four diverse AIV isolates for use as vaccines in chickens, including two commercial vaccines and two additional contemporary isolates, against challenge with numerous clade 2.2.1 and clade 2.2.1.1 H5N1 HPAIV Egyptian isolates to assess the variation in protection among different vaccine and challenge virus combinations.
  
  
  METHODS
  Vaccination-challenge studies with four vaccines and up to eight challenge strains with each vaccine for a total of 25 vaccination-challenge groups were conducted with chickens. An additional eight groups served as sham-vaccinated controls. Mortality, mean death time, morbidity, virus, and pre-challenge antibodies were evaluated as metrics of protection. Hemagglutination inhibition data were used to visualize the antigenic relatedness of the isolates.
  
  
  CONCLUSIONS
  Although all but one vaccine-challenge virus combination significantly reduced shed and mortality as compared to sham vaccinates, there were differences in protection among the vaccines relative to one another based on challenge virus. This emphasizes the difficulty in vaccinating against diverse, evolving virus populations, and the importance of selecting optimal vaccine seed strains for successful HPAIV control.
authors.affiliation: Southeast Poultry Research Laboratory, USDA-ARS, Athens, GA, USA.
authors.forename: Erica
authors.initials: E
authors.lastname: Spackman
authors.forename: David E
authors.initials: DE
authors.lastname: Swayne
authors.forename: Mary J
authors.initials: MJ
authors.lastname: Pantin-Jackwood
authors.forename: Xiu-Feng
authors.initials: XF
authors.lastname: Wan
authors.forename: Mia K
authors.initials: MK
authors.lastname: Torchetti
authors.forename: Mohammad
authors.initials: M
authors.lastname: Hassan
authors.forename: David L
authors.initials: DL
authors.lastname: Suarez
authors.forename: Mariana
authors.initials: M
authors.lastname: Sá e Silva
mesh_terms: D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D002645:Chickens; D004534:Egypt; D006385:Hemagglutination Inhibition Tests; D053124:Influenza A Virus, H5N1 Subtype / Q000276:immunology*; D005585:Influenza in Birds / Q000473:pathology / Q000517:prevention & control* / Q000821:virology*; D011200:Poultry; D016019:Survival Analysis; D016896:Treatment Outcome; D014612:Vaccines / Q000008:administration & dosage / Q000276:immunology*; D017201:Virus Shedding
chemical_list: D000914:Antibodies, Viral; D014612:Vaccines
keywords: H5N1; highly pathogenic avian influenza virus; poultry vaccination