Comparison of primary vaccination regimes for equine influenza: working towards an evidence-based regime.
Authors: Cullinane A, Gildea S, Weldon E
Journal: Equine veterinary journal
Summary
# Equine Influenza Vaccination: Optimising Primary Immunisation Schedules Understanding which vaccination intervals best protect horses against equine influenza remains essential for safeguarding both individual animals and population health, yet international regulatory requirements have historically diverged without robust scientific comparison. Cullinane and colleagues conducted a randomised, prospective trial in 55 seronegative horses comparing three primary vaccination regimes—minimal intervals (racing authority minimum), manufacturer-recommended intervals, and maximal intervals (racing authority maximum)—using a subunit immune stimulating complex-based vaccine and measuring antibody responses via single radial haemolysis. Whilst lengthening vaccination intervals between first, second and third doses did increase periods of susceptibility to infection, immune responses to the second and third vaccinations remained comparable across all regimes, with notably poor responders identified particularly amongst yearlings, and superior responses observed in 2- and 3-year-olds compared to younger age groups. Extended intervals may paradoxically offer practical advantages by allowing strategic vaccination timing around anticipated exposure periods, despite temporarily widening immunity gaps. These findings provide evidence-based data urgently needed to align international vaccination standards, and suggest that age-specific response patterns merit consideration in future vaccination protocols, particularly regarding early-year vaccinations of younger horses.
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Practical Takeaways
- •Longer vaccination intervals permitted by racing authorities create periods of increased susceptibility to equine influenza, requiring strategic timing around exposure risk periods
- •Poor responders to initial vaccination are common in yearlings, suggesting this age group may need additional monitoring or alternative vaccination strategies
- •Vaccination schedules can be extended without compromising immune response to booster doses, allowing flexibility in management planning
Key Findings
- •Longer vaccination intervals increase immunity gaps between doses but do not inhibit antibody response to second and third vaccinations
- •Response to second and third doses was similar regardless of vaccination regime used
- •Yearlings had the greatest number of poor responders to initial vaccination compared to other age groups
- •2- and 3-year-old horses showed superior vaccination responses compared to weanlings and yearlings