Comparison of two modern vaccines and previous influenza infection against challenge with an equine influenza virus from the Australian 2007 outbreak

Abstract

During 2007, large outbreaks of equine influenza (EI) caused by Florida sublineage Clade 1 viruses affected horse populations in Japan and Australia. The likely protection that would be provided by two modern vaccines commercially available in the European Union (an ISCOM-based and a canarypox-based vaccine) at the time of the outbreaks was determined. Vaccinated ponies were challenged with a representative outbreak isolate (A/eq/Sydney/2888-8/07) and levels of protection were compared. A group of ponies infected 18 months previously with a phylogenetically-related isolate from 2003 (A/eq/South Africa/4/03) was also challenged with the 2007 outbreak virus. After experimental infection with A/eq/Sydney/2888-8/07, unvaccinated control ponies all showed clinical signs of infection together with virus shedding. Protection achieved by both vaccination or long-term immunity induced by previous exposure to equine influenza virus (EIV) was characterised by minor signs of disease and reduced virus shedding when compared with unvaccinated control ponies. The three different methods of virus titration in embryonated hens’ eggs, EIV NP-ELISA and quantitative RT-PCR were used to monitor EIV shedding and results were compared. Though the majority of previously infected ponies had low antibody levels at the time of challenge, they demonstrated good clinical protection and limited virus shedding. In summary, we demonstrate that vaccination with current EIV vaccines would partially protect against infection with A/eq/Sydney/2888-8/07-like strains and would help to limit the spread of disease in our vaccinated horse population.

ISCOM-based equine influenza vaccine: Duration of immunity and randomised clinical trials to assess an accelerated schedule of immunisation and efficacy

“…At this time, ponies showed little or undetectable SRH antibody titre [10]. It is likely that protection in absence of antibodies involved CMI stimulation, which efficiently supports or replaces protection induced by antibodies [10,43,44]. Stimulation of IFN gamma, a CMI marker, was previously demonstrated after immunization with ISCOM and ISCOMatrix EI [9,45,46].…”

“…Those same four ponies were significantly protected against clinical signs of disease and virus shedding when re-infected with A/eq2/Sydney2888-8/07, 18 months after initial contact with A/eq2/South Africa/4/03. At this time, ponies showed little or undetectable SRH antibody titre [10]. It is likely that protection in absence of antibodies involved CMI stimulation, which efficiently supports or replaces protection induced by antibodies [10,43,44].…”

“…Equip FT is the same vaccine complemented with the TT antigen. The Equip F ISCOM-based EI vaccine has been shown to stimulate both humoral and CMI [9] and to provide significant protection when tested at the peak of immunity (2 weeks after the second immunisation) against the representative outbreak EIV strains A/eq/South Africa/4/03 [9] and A/eq/Sydney/288-8/07 [10] of the Florida clade 1 sublineage [11][12][13]. This EI vaccine contains H3N8 EIV isolates (A/eq/Borlange/91 and A/eq/Kentucky/98; H3N8; European and American lineages, respectively), which present antigenic and genetic differences from the current Florida clade 2 EIV strains circulating in Europe or the Florida clade 1 isolates predominantly circulating in the US [12,14,15].…”

Facing the threat of equine influenza

“…This is one of the approaches used to control the outbreak in Australia in 2007. Work sponsored by the HBLB showed vaccines available in the UK in 2007 were able to partially protect against the 2007 Australian outbreak virus, if it was to have arrived on our shores (Bryant et al . 2009a).…”

“…Natural infection with EIV has been shown to induce long‐term immunity independent of circulating antibodies against HA in the horse (Hannant et al. 1988; Bryant et al . 2009a).…”