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Characteristics of the CEVA Vectormune HVT-AIV Vaccine

  

May 21, 2015

    

The use of a vaccine as an adjunct to existing control measures in the face of devastating mortality from H5N2 highly pathogenic avian influenza implies a consideration of available vaccines.  CEVA Vectormune HVT-AIV is reviewed for the benefit of subscribers to EGG-CITE the key facts are summarized:-

Characteristics of the CEVA Vectormune HVT-AIV Vaccine

The use of a vaccine as an adjunct to existing control measures in the face of devastating mortality from H5N2 highly pathogenic avian influenza implies a consideration of available vaccines.  CEVA Vectormune HVT-AIV is reviewed for the benefit of subscribers to EGG-CITE the key facts are summarized:-

  • Vectormune HVT-AIV is a recombinant, avian influenza vaccine using the herpes virus of turkeys (HVT) as the vector.  To produce the vaccine the hemagglutinin (HA) gene of an H5N1 avian influenza virus was inserted into the genome of HVT. After administration HVT replicates with expression of the HA gene, inducing immunity.
  • The vaccine will provide substantial protection (between 70 and 95 percent) against virulent challenge under field conditions.  The vaccine will not prevent but will significantly reduce shedding should vaccinated flocks be challenged.
  • Since HVT is apathogenic no adverse effects are associated with administration of the vector virus.
  • The HA gene inserted into the HVT vector was derived from highly pathogenic H5N1strain isolated from a swan in 2006 but was altered to express the amino acid sequence at the cleavage site characteristic of a low-pathogenic avian influenza virus.
  • The vaccine is registered in the U.S. and could be administered subject to availability and with the approval and limitations imposed by the USDA-APHIS.
  • The vaccine will stimulate immunity when administered in ovo or at day-old in the hatchery even to chicks with maternal antibody again HVT.
  • Vectormune HVT-AIV has been shown to be effective against both H5NI and H5N2 highly pathogenic strains of avian influenza. To date under field conditions continuous efficacy has been demonstrated in Egypt and Mexico.
  • Since herpes virus continually replicates, it is anticipated that long-lived breeder and egg-producing hens will be protected for their entire life.
  • Durable immunity is established between two and three weeks after administration as with any HVT cell-associated vaccine but subject to the same restraints and precautions applied to conventional HVT vaccine.
  • Efficacy, host challenge and shed rates have been verified in the U.S. at the Southeast Poultry Research Laboratory and results have been published in a peer review journal* and company literature in addition to presentations at international scientific meetings.
  • HVT-vector vaccines have been shown to be superior to pox-vector vaccines due to the universal presence of material antibodies against avian pox.  Inactivated oil emulsion vaccines to be effective must be homologous with the challenge strain and must be manufactured according to accepted protocols to achieve safety and efficacy.
  • Vaccinated chickens will demonstrate H antibodies applying the hemagglutination assay.  Infected flocks can be differentiated from vaccinated flocks by application of the ELISA-based assay which detects viral nucleoprotein. This combination of assays can be used to differentiate between exposed and infected flocks independently of demonstrating viral RNA by PCR in peracute cases. The ELISA assay will be positive in the event of a naturally exposed flock and will be negative in vaccinated flocks consistent with the DIVA principle.

Subscribers are referred to the EGG-CITE Editorial on May 15th which reviewed the benefits and negative considerations relating to a change in APHIS policy to allow vaccination.

* Kapczynski, D. et al Vaccine protection of chickens against antigenically diverse H5 highly pathogenic avian influenza isolates with a live HVT vector vaccine expressing the influenza hemagglutinin gene derived from a clade 2.2avian influenza. Vaccine. 33:1197-1205 (2015)