A comparison of antibody responses to commercial equine influenza vaccines following annual booster vaccination of National Hunt horses – a randomised blind study.
Abstract: Protection against equine influenza virus (EIV) relies largely on the production of circulating antibodies specific for the haemagglutinin (HA) glycoprotein. The objective of this study was to determine the antibody response of National Hunt horses in training to booster vaccination. The antibody response to the six equine influenza vaccines available in Ireland (three whole inactivated vaccines, two subunit vaccines and a canary pox recombinant vaccine), was monitored by single radial haemolysis (SRH) for six months post vaccination. There was no significant difference between antibody response induced following booster vaccination with any of the six vaccines. The antibodies peaked between two and four weeks post vaccination, decreased significantly by three months post vaccination and declined to their original levels by six months post vaccination. Peak antibody response to the canary pox recombinant vaccine was delayed in comparison to the other vaccines. Although analysis of the mean SRH levels of the horses suggested that they were clinically protected post booster vaccination, analysis of the individual responses suggested that there was potential for vaccination breakdown in a manner similar to that observed previously in racing yards in Ireland. There was a significant correlation between the SRH level at the time of vaccination and the antibody response. The findings of the study suggest that it would be advantageous to monitor SRH levels and to vaccinate strategically. The revaccination of horses with low antibody levels three months post booster vaccination may have been more effective in protecting horses in this yard than the annual vaccination of horses with high SRH levels. Eighteen of the 44 (41%) horses included in this study did not demonstrate a significant rise in SRH level to H3N8 following booster vaccination. It is presumed that annual revaccination is the minimum necessary to protect all horses against EI but this assumption needs to be systematically evaluated. It has been demonstrated that shorter intervals are required for optimum protection of young horses and it may be that longer vaccination intervals are sufficient for older horses with several years of vaccination history. Further investigations in a larger population of horses will be necessary to determine if the findings of this study are applicable to the population at large.
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The study investigated the effectiveness of six different equine influenza vaccines in National Hunt horses in Ireland by monitoring the antibody response over six months. Despite variation in initial reactions, there was no significant difference in the antibody response induced by any of the vaccines.
Research Methodology
The research used a randomised blind method to compare the antibody response to six different equine influenza vaccines available in Ireland. This ensured that bias in the experiment was minimised.
The antibodies were monitored by a process called single radial haemolysis (SRH) for six months after vaccination.
The study enrolled 44 National Hunt horses in Ireland for this experiment.
Findings
There was no significant difference found in the antibody response induced by any of the vaccines. All participants reached their peak antibody response within two to four weeks of vaccination, and this level fell to their original levels by six months after vaccination.
Peak antibody response to the canary pox recombinant vaccine was delayed compared to the other vaccines.
Based on the average SRH levels, it seemed that the horses were clinically protected after the booster shot. However, analysis of individual responses suggested potential for vaccination breakdown, reminiscent of previous incidents in Irish racing yards.
There was a significant relation between the SRH level at the time of vaccination and the antibody response, suggesting that monitoring SRH levels and strategising vaccination accordingly could prove beneficial.
Implications and Further Studies
The results suggested that horses with low initial antibody levels may benefit from revaccination three months after the initial booster vaccination, instead of an annual vaccination as traditionally done.
18 out of the 44 horses in the study did not show a significant rise in SRH level to H3N8 influenza virus following the booster vaccination. This suggests that the current approach of annual revaccination might not be sufficient for all horses against equine influenza (EI) and needs to be evaluated systematically.
The study also puts forth that shorter vaccination intervals might be necessary for young horses, while longer intervals might suffice for older horses with a history of vaccination.
Additional research in larger horse populations will be necessary to confirm the findings of the study and their applicability to broader horse populations.
Cite This Article
APA
Gildea S, Arkins S, Walsh C, Cullinane A.
(2011).
A comparison of antibody responses to commercial equine influenza vaccines following annual booster vaccination of National Hunt horses – a randomised blind study.
Vaccine, 29(22), 3917-3922.
https://doi.org/10.1016/j.vaccine.2011.03.003