Annual booster vaccination and the risk of equine influenza to Thoroughbred racehorses.
Authors: Gildea Sarah, Lyons Pamela, Lyons Rachel, Gahan Jacinta, Garvey Marie, Cullinane Ann
Journal: Equine veterinary journal
Summary
# Editorial Summary: Annual Booster Vaccination and Equine Influenza Risk in Thoroughbred Racehorses A 2020 outbreak of equine influenza across four Irish racing yards—occurring within a four-week period—prompted Gildea and colleagues to investigate vaccination effectiveness and biosecurity practices in what proved to be a sobering epidemiological analysis. The team collected vaccination records and clinical samples from 118 horses across the affected premises, tracking viral spread amongst populations with apparently compliant vaccination histories. Despite all index cases being vaccinated according to Turf Club regulations, vaccine breakdown occurred in 27 of 80 horses (33.8%) with up-to-date records; critically, two-thirds of these horses hadn't received a booster within six months, and 37% were actually due their annual booster at the time of clinical presentation. Beyond vaccination gaps, inadequate biosecurity following horse movements and mixing of vaccinated racing stock with poorly protected non-racing populations substantially amplified transmission. The findings challenge reliance on annual-only boosters as sufficient protection and indicate that more frequent vaccination schedules—particularly for younger horses—combined with co-ordinated yard-wide vaccination timing to avoid vulnerable periods, warrant serious consideration for equestrian professionals managing high-risk populations.
Read the full abstract on PubMed
Practical Takeaways
- •Annual booster vaccination alone is insufficient protection against equine influenza—consider more frequent booster protocols, especially for young horses in racing yards
- •Implement strict biosecurity measures when introducing new horses or after horses return from events, and avoid mixing racing and non-racing populations with different vaccination histories
- •Synchronize vaccination schedules across yards sharing horses to reduce high-risk periods for virus transmission and monitor for vaccine failure even in compliant horses
Key Findings
- •Vaccine breakdown occurred in 27/80 (33.8%) horses with up-to-date vaccination records across all vaccine products
- •66.7% of horses with vaccine breakdown had not received booster vaccination within 6 months, and 37% were due annual booster at time of clinical signs
- •Biosecurity failures, horse movement within premises, and mixing of vaccinated and unvaccinated populations facilitated virus transmission despite vaccination
- •Index cases on all affected premises were vaccinated in accordance with racing authority rules, indicating vaccine failure in compliant populations