Comparison of primary vaccination regimes for equine influenza: Working towards an evidence‐based regime

Abstract

SummaryReasons for performing study: Vaccination is crucial to the control of equine influenza (EI). The study was conducted in an effort to lay the groundwork for achieving international harmonisation of regulatory requirements based on scientific evidence of performance of different vaccination regimes. Objectives: To evaluate the effectiveness of 3 different primary vaccination regimes: vaccination with the minimal intervals permitted by the racing authorities; vaccination in accordance with the manufacturer's instructions and vaccination with the longest intervals permitted by the racing authorities. Study design: Randomised, prospective clinical trial. Methods: The 55 seronegative unvaccinated horses in this study were subdivided by age and randomly allocated one of the 3 vaccination regimes. All groups were sampled each time a group was vaccinated and 3-5 weeks post vaccination. Horses were vaccinated with a subunit immune stimulating complex-based vaccine (Equip FT). Antibodies against EI were measured by single radial haemolysis. Results: Lengthening the vaccination intervals increased the immunity gaps between first (V1) and second (V2) doses, and V2 and third dose (V3) but did not inhibit the response to V2 and V3. The response to V2 and V3 was similar irrespective of the regime. Poor responders to V1 were identified in all age groups included in this study but the greatest number of poor responders was among the yearlings. The 2-and 3-year-old horses responded better to vaccination than the weanlings or yearlings. Conclusions: Longer vaccination intervals permitted by racing authorities increase the periods of susceptibility to EI but they may facilitate strategic vaccination prior to times of increased risk of exposure to virus. The study provides the type of evidence-based data necessary to commence meaningful discussion of international harmonisation of EI vaccination requirements.

Whole‐genome sequencing and antigenic analysis of the first equine influenza virus identified in Turkey

“…Vaccination with epidemiologically relevant EIV strains activates the adaptive immune response and provides clinical and virological protection against potential future EIV infection . Strategic vaccination preceding travel and participation in racing events optimises antibody levels during periods of heightened risk of exposure . However, periods of immunological susceptibility and the mixing of naïve horses with vaccinated horses can lead to outbreaks of influenza .…”

“…35 Strategic vaccination preceding travel and participation in racing events optimises antibody levels during periods of heightened risk of exposure. 37 However, periods of immunological susceptibility and the mixing of naïve horses with vaccinated horses can lead to outbreaks of influenza. 38,39 It is preferable to apply mandatory vaccination to all horses that enter a facility irrespective of their activities as seronegative horses are frequently the index case in an outbreak.…”

A Systematic Review of Recent Advances in Equine Influenza Vaccination

“…This specific vaccine was also shown to induce the highest levels of SRH antibody when compared with other EI vaccines, which could provide an explanation for the lower percentage of poor responder reported after first immunisation [ 79 , 82 ]. The age at the time of first vaccination also seems to influence the response to immunisation [ 151 ], with reduced EI vaccine immunogenicity in weanling and yearlings when compared with older horses [ 151 ]. Antibody titres are usually back to normal levels after the second immunisation.…”

“…, minimum intervals permitted by racing authorities, product labels recommended and longest intervals allowed). Results from this study indicated that overall levels of SRH antibody reached at peaks of immunity were not significantly affected by the nature of the vaccination regimes, however, the duration of the period of susceptibility between V1 and V2, and subsequently V2 and V3 were significantly lengthened when the longest interval scheduled was applied [ 151 ] (study sponsored by the Irish Department of Agriculture). This study confirms that product’s label recommendations should be preferred, when possible.…”

Strategic implementation of vaccines for control of equine influenza

“…Cullinane et al . tested three different primary vaccination schedules as follows: (1) at the minimal intervals stipulated by the racing authorities (i.e. 3 weeks between the first two doses and 5 months before the third dose); (2) according to the vaccine manufacturer's recommendations (i.e.…”