Efficacy of a cold-adapted, intranasal, equine influenza vaccine: challenge trials.
Authors: Townsend H G, Penner S J, Watts T C, Cook A, Bogdan J, Haines D M, Griffin S, Chambers T, Holland R E, Whitaker-Dowling P, Youngner J S, Sebring R W
Journal: Equine veterinary journal
Summary
# Editorial Summary: Cold-adapted Intranasal Equine Influenza Vaccine Efficacy Researchers evaluated a temperature-sensitive, modified-live influenza vaccine administered intranasally to determine its protective capacity against natural infection. Ninety influenza-naive foals were randomised into vaccinated (n=60) and control (n=30) groups across three separate aerosol challenge timepoints—at 5 weeks, 6 months, and 12 months post-vaccination—with daily clinical monitoring, nasal viral shedding samples, and serological assessment over a 14-day period following each challenge. Vaccinated animals demonstrated significantly reduced clinical signs and fever at both 5-week (P=0.0001 and P=0.0008 respectively) and 6-month challenges (P=0.005 and P=0.0007), whilst viral shedding was substantially lower in duration and concentration across all three timepoints, with the most pronounced protection observed at the earlier challenge dates. Importantly, protection remained clinically meaningful at 12 months post-vaccination, with reduced temperature elevation and virus shedding despite some waning of immunity. For practitioners managing vaccination programmes in naive or at-risk populations, this evidence suggests a single intranasal dose offers robust short-to-medium-term protection against clinical disease severity and transmission potential, though timing of booster vaccinations warrants consideration for year-round immunity in high-exposure environments.
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Practical Takeaways
- •A single intranasal dose of this cold-adapted vaccine provides meaningful protection against clinical influenza for at least 6 months, substantially reducing disease severity even when horses face live-virus challenge
- •Vaccinated horses shed significantly less virus over shorter periods, reducing transmission risk within premises and supporting herd-level disease control
- •This vaccine offers an effective tool to reduce the frequency, severity and duration of influenza outbreaks in North American equine operations without adverse vaccination effects
Key Findings
- •At 5 weeks post-vaccination, vaccinated foals showed significantly lower clinical scores (P=0.0001), smaller temperature increases (P=0.0008), and reduced virus shedding (P<0.0001) compared to controls
- •At 6 months post-vaccination, vaccine efficacy remained significant with reduced clinical scores (P=0.005), temperature increases (P=0.0007), and virus shedding (P=0.03)
- •At 12 months post-vaccination, rectal temperatures, duration and concentration of virus shed remained significantly reduced in vaccinated animals (P=0.006, P=0.03, and P=0.04 respectively)
- •No adverse reactions to vaccination were observed in any of the 90 foals tested