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

The widespread use of equine influenza (EI) vaccines plays an important role in the prevention and control of EI outbreaks. Vaccine strain updates, optimisation of immunisation schedules, and frequent evaluation of vaccine efficacy are necessary to maintain an acceptable level of protection and overall disease control. Results from three independent vaccine studies are reported here.Study 1: duration of immunity (exploratory research). The antibody and interferon (IFN) gamma response induced by an ISCOM (Immuno-Stimulating COMplex)-based EI vaccine (Equip F®), was measured in a group of 4 ponies up to one year after booster immunisation and compared to immunity induced by equine influenza virus (EIV) infection. The antibody and IFN gamma responses kinetics were defined and levels were similar to those induced by experimental EIV infection.Study 2: accelerated schedule of immunisation (randomised trial). Most EI vaccines require a 4–6 week interval during the primary two dose course of immunisation, during which time most animals remain susceptible to EIV infection. The immunogenicity and safety of the ISCOM-based EI + tetanus vaccine (Equip FT) with a 3-week accelerated immunisation interval was evaluated and compared to the recommended six-week vaccination interval in order to improve flexibility and to reduce the period of susceptibility. The antibody responses to the vaccine antigens (tetanus toxoid and EIV) were measured up to 2 weeks after the first booster vaccination (V3). The 3-week accelerated primary course interval was well tolerated and serology results suggested good immunogenicity against both EIV and tetanus antigens.Study 3: efficacy against Florida clade 2 EIV strain (randomised trial). Efficacy against the representative Florida clade 2 strain A/eq/Richmond/1/07 was also evaluated at the peak of immunity, shortly after 2nd vaccination (V2). Six ponies were vaccinated with EquipFT according to label (6-week interval between first and second injection) and 6 control ponies received saline injections. Sixteen days after V2 (day 58), all animals were experimentally infected with A/eq/Richmond/1/07. Clinical signs of disease and virus shedding were assessed for 14 days and found to be significantly reduced in vaccinated animals.