Elanco has announced the results of a challenge study which the company says demonstrates the ability of Duvaxyn IE-T Plus equine influenza vaccine to cross protect against A/equi-2/Richmond/1/07 (H3N8) two weeks after a two dose primary course¹.

The study, conducted by the Animal Health Trust, involved two groups of EIV seronegative horses. The first group, consisting of seven vaccinates, were given two dose of Duvaxyn IE-T Plus, 28 days apart, and challenged with A/equi-2/Richmond/1/07 (H3N8) virus strain 14 days after the second vaccination. The second group of unvaccinated horses was challenged at the same time. Duvaxyn IE-T Plus caused a statistically significant reduction in both clinical signs of the disease and in viral shedding.

According to Elanco, this is believed to be the first demonstration of cross protection by a current UK equine influenza vaccine against a Florida sub-lineage clade 2 reference strain.

The OIE (World Organisation for Animal Health) updated its equine influenza vaccine recommendations in 2010 to reflect the fact that all field strains characterised through 2008 and 2009 were of clade 1 or 2 of the Florida sub-lineage. The antigenic difference between viruses of these clades could potentially compromise the effectiveness of vaccines containing a representative of a single clade².

Anna Jackson, national veterinary manager for Elanco Companion Animal Health, said:  "Whilst no vaccine has been updated to match the current OIE recommendations, the results of this challenge study provide reassurance that horses vaccinated with Duvaxyn will be protected against clinical signs of disease caused by currently circulating strains of equine influenza, including those the OIE have identified as being of concern."

Duvaxyn IE-T Plus is an inactivated whole virus equine influenza vaccine, adjuvanted with an aqueous-based adjuvant. Elanco says that experts in the field of human vaccination have expressed the view that whole virus vaccines have the potential to induce a stronger and more broadly-based response to circulating influenza strains than those contained in sub-unit vaccines because of the presence of the full set of virus proteins in the vaccine³.

References:

• 1. ECAH study: AHT study ID C012/01
• 2. OIE. Office International des Epizooties Bulletin (2010), 2 pp.44-45
• 3. Meeting Notes: 3rd WHO meeting on evaluation of pandemic influenza prototype vaccines in clinical trials, 15-16 February 2007, WHO, Geneva

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