Efficacy, duration, and onset of immunogenicity of a West Nile virus vaccine, live Flavivirus chimera, in horses with a clinical disease challenge model.
Authors: Long M T, Gibbs E P J, Mellencamp M W, Bowen R A, Seino K K, Zhang S, Beachboard S E, Humphrey P P
Journal: Equine veterinary journal
Summary
# Editorial Summary: West Nile Virus Live Chimera Vaccine Protection in Horses West Nile virus remains a significant neurological threat to equine populations and humans, prompting the development of more effective preventative strategies. Researchers evaluated a novel live Flavivirus chimera vaccine by comparing clinical outcomes, viraemia, and histopathological changes in vaccinated versus control horses following intrathecal WNV challenge at 10 days, 28 days, and 12 months post-vaccination. Protection was evident by day 28, with only 1 of 20 vaccinated horses developing severe clinical signs compared to 10 of 10 controls (P<0.01), and this immunity persisted at 12 months, where 1 of 9 vaccinated horses showed severe disease versus 8 of 10 controls (P<0.05). Critically, vaccinated horses demonstrated minimal or absent viraemia and substantially reduced histopathological lesions across all challenge timepoints, including early protection at day 10 (5 of 6 vaccinated horses with moderate-to-severe signs versus all 3 controls). For equine practitioners, this represents the first USDA-licensed WNV vaccine validated against a severe, field-realistic challenge model with demonstrated 12-month duration of immunity—information essential for informed vaccination protocols and owner counselling on disease prevention and encephalitis risk reduction.
Read the full abstract on PubMed
Practical Takeaways
- •A single dose of WN-FV vaccine provides robust protection against clinical West Nile virus disease in horses for at least 12 months, with most protection evident from day 28 onwards
- •Vaccinated horses are unlikely to develop viraemia even if exposed to WNV, reducing disease transmission risk and severity of neurological complications
- •This vaccine has been USDA-licensed with a 12-month duration of immunity claim based on severe challenge testing, making it a reliable option for WNV prevention in equine populations
Key Findings
- •Single vaccination with WN-FV chimera vaccine protected 19/20 vaccinated horses versus 0/10 control horses at day 28 post-vaccination challenge (P<0.01)
- •Protective immunity persisted for 12 months, with 8/9 control horses showing severe clinical signs versus only 1/9 vaccinated horses at 12-month challenge (P<0.05)
- •Vaccinated horses developed no viraemia at day 28 challenge timepoint while all control horses did, with minimal histopathological lesions in vaccinated group
- •Immune response onset demonstrated within 10 days post-vaccination, though protection was more robust by day 28