Abstract
Vaccination is an effective tool to limit equine influenza virus (EIV H3N8) infection, a contagious respiratory disease with potentially huge economic impact. The study assessed the effects of antigenic change on vaccine efficacy and the need for strain update. Horses were vaccinated (V1 and V2) with an ISCOMatrix-adjuvanted, whole inactivated virus vaccine (Equilis Prequenza, group 2, FC1 and European strains) or a carbomer-adjuvanted, modified vector vaccine (ProteqFlu, group 3, FC1 and FC2 HA genes). Serology (SRH, HI, VN), clinical signs and viral shedding were assessed in comparison to unvaccinated control horses. The hypothesis was that group 2 (no FC2 vaccine strain) would be less well protected than group 3 following experimental infection with a recent FC2 field strain (A/equi-2/Wexford/14) 4.5 months after vaccination. All vaccinated horses had antibody titres to FC1 and FC2. After challenge, serology increased more markedly in group 3 than in group 2. Vaccinated horses had significantly lower total clinical scores and viral shedding. Unexpectedly, viral RNA shedding was significantly lower in group 2 than in group 3. Vaccination induced protective antibody titres to FC1 and FC2 and reduced clinical signs and viral shedding. The two tested vaccines provided equivalent protection against a recent FC2 EIV field strain.
Highlights
Equine influenza (EI), caused by equine influenza virus (EIV), is highly contagious and is one of the major viral respiratory diseases in horses [1]
The aim was to provide insight into the impact of vaccine type and minor antigenic differences between vaccine and field strains on vaccine efficacy, after challenge during the most susceptible period
The study showed that the two vaccines were very similar based on induced protective antibody titres (single radial haemolysis (SRH), haemagglutination inhibition (HI) and virus neutralisation (VN)) to FC1 and FC2 strains and in reducing clinical signs and viral shedding of EIV, and they provide equal protection to EIV strains currently circulating in the horse population
Summary
Equine influenza (EI), caused by equine influenza virus (EIV), is highly contagious and is one of the major viral respiratory diseases in horses [1]. These apparently large antigenic differences in EIV may not be biologically significant in horses [20,21] This has already been observed for avian influenza where the vaccine is capable of providing sufficient protection against infection with new field strains the vaccine virus strain differs from field virus [22,23]. The study showed that the two vaccines were very similar based on induced protective antibody titres (single radial haemolysis (SRH), haemagglutination inhibition (HI) and virus neutralisation (VN)) to FC1 and FC2 strains and in reducing clinical signs and viral shedding of EIV, and they provide equal protection to EIV strains currently circulating in the horse population
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