An Evaluation of Three Different Primary Equine Influenza Vaccination Intervals in Foals.
Authors: Dilai Mohamed, Fassi Fihri Ouafaa, El Harrak Mehdi, Bouchiba Anouar, Dehhaoui Mohammed, Mahir Wissal, Dikrallah Asmaa, Legrand Loïc, Paillot Romain, Piro Mohammed
Journal: Journal of equine veterinary science
Summary
# Editorial Summary: Primary Equine Influenza Vaccination Intervals in Foals Equine influenza vaccination protocols in foals typically follow standard guidelines, yet the optimal spacing between primary doses remains debated among practitioners. Researchers vaccinated 21 unvaccinated thoroughbred foals in three groups with different primary intervals—one, two, or three months between first and second doses—and tracked antibody responses using single radial hemolysis assay for 12 months following the third dose administered six months after the second. Whilst all foals achieved clinical protection within two weeks of the second dose and maintained it through the study period, the shorter one-month interval produced a lower immunity peak (158.05 mm²) after the second vaccination and a wider 18-week protection gap before the third dose, compared with the three-month interval group (221.45 mm² and 12 weeks respectively). For practitioners, this suggests that whilst accelerated one-month protocols offer earlier initial protection—valuable for foals entering training or competition—the reduced antibody titre and extended immunity window creates vulnerability; the two- to three-month intervals provide superior peak immunity and shorter unprotected periods, meriting consideration for foals in lower-risk environments or where vaccination flexibility permits.
Read the full abstract on PubMed
Practical Takeaways
- •While shorter vaccination intervals (1 month) achieve protective immunity faster in foals, a 3-month interval between first and second doses produces stronger peak antibody levels and more reliable protection during the gap before the third dose
- •Practitioners should consider the 2-3 month interval range for primary foal vaccination to balance early protection with antibody durability and reduced window of vulnerability
- •All tested intervals achieved adequate protection, so choice can be individualized based on management schedule and risk assessment, but avoid the shortest (1-month) interval if foals face high disease exposure risk
Key Findings
- •All foals seroconverted and exceeded clinical protection threshold by 2 weeks after second vaccination (V2) and maintained protection through 1 year post-third vaccination (V3)
- •One-month primary vaccination interval produced lower immunity peak after V2 (158.05 ± 6.63 mm²) compared to two-month (174.72 ± 6.86 mm²) and three-month (221.45 ± 14.48 mm²) intervals
- •One-month interval group experienced wider immunity gap between V2 and V3 (18 weeks) versus two-month (16 weeks) and three-month (12 weeks) intervals
- •Three-month primary vaccination interval demonstrated superior peak antibody response and shortest immunity gap, despite one-month interval achieving earlier protective immunity