Safety of an attenuated West Nile virus vaccine, live Flavivirus chimera in horses.
Authors: Long M T, Gibbs E P J, Mellencamp M W, Zhang S, Barnett D C, Seino K K, Beachboard S E, Humphrey P P
Journal: Equine veterinary journal
Summary
# West Nile Virus Vaccine Safety in Horses West Nile virus remains a significant endemic disease threat to naive equine populations, necessitating rigorous safety evaluation of new immunisation strategies. Long and colleagues conducted three complementary safety protocols: an overdose and viral shedding study (100× immunogenicity dose with sentinel horse contact), a reversion-to-virulence assessment (20× overdose with serial passage monitoring), and a field safety trial encompassing 919 horses of varied ages, breeds and sex. Across all protocols, the attenuated West Nile Flavivirus chimera vaccine induced neither local nor systemic adverse reactions, produced no detectable viral shedding, showed no tissue dissemination and demonstrated complete genetic stability with no reversion to pathogenic phenotypes. Notably, vaccinating several hundred horses—many with prior WNV exposure or previous vaccination—resulted in no adverse events. These findings provide strong evidence that this live attenuated chimeric vaccine offers a safe immunoprophylactic option for equine West Nile disease prevention, particularly relevant for practitioners managing populations in endemic regions or those with disease exposure risk.
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Practical Takeaways
- •WN-FV chimera vaccine is safe for use in horses including those potentially previously exposed to WNV, with no adverse effects observed even at extremely high doses
- •Vaccinated horses pose no transmission risk to unvaccinated horses as there is no vaccine virus shedding
- •This vaccine represents a safe immunoprophylaxis option against West Nile virus disease in equine populations
Key Findings
- •WN-FV chimera vaccine produced no site or systemic reactions in vaccinated horses at 100x immunogenicity overdose
- •No vaccine virus shedding detected and no spread to sentinel horses housed with vaccinated animals
- •No reversion to virulence observed following passage in horses vaccinated with 20x overdose
- •Field safety testing of 919 horses across various ages, breeds and sex showed no untoward reactions