Comparison of hamster and pony challenge models for evaluation of effect of antigenic drift on cross protection afforded by equine influenza vaccines.
Authors: Daly J M, Yates R J, Browse G, Swann Z, Newton J R, Jessett D, Davis-Poynter N, Mumford J A
Journal: Equine veterinary journal
Summary
# Editorial Summary: Hamster versus Pony Models for Equine Influenza Vaccine Challenge Studies Determining whether vaccine strains remain protective against circulating field viruses is critical for equine influenza control, yet pony challenge experiments are resource-intensive and ethically demanding. Daly and colleagues compared cross-protection data from hamsters and ponies vaccinated with inactivated H3N8 vaccines representing strains from 1963–1989, then challenged with a 1989 isolate, to evaluate whether small animal models could predict real-world vaccine efficacy. Whilst ponies showed no significant difference in viral shedding between homologous and heterologous vaccine groups, hamsters immunised with older, antigenically distant strains demonstrated significantly higher lung viral titres than those receiving matched vaccines—a finding paralleled in both species by increased virus excretion when vaccine strains were older. Although the hamster model lacked the quantitative sensitivity of pony studies in measuring viral shedding, both systems yielded the same qualitative conclusion: heterologous vaccines provide reduced protection against virus excretion compared with homologous vaccines, suggesting antigenic drift substantially compromises cross-protection. For practitioners and vaccine developers, this validates the hamster model as a preliminary screening tool for assessing vaccine strain relevance before committing to expensive pony trials, though further refinement and validation work would strengthen its predictive reliability for field performance.
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Practical Takeaways
- •Equine influenza vaccines containing strains matched to currently circulating viruses are likely to provide better protection against virus shedding than older vaccine strains, supporting regular vaccine strain updates
- •While pony challenge studies remain the gold standard for vaccine evaluation, hamster models may offer a faster and more feasible preliminary assessment tool for vaccine efficacy before committing to expensive pony studies
- •Vaccination programs should account for antigenic drift over time; vaccines developed from older virus isolates may offer reduced protection against contemporary challenge strains
Key Findings
- •Hamsters vaccinated with heterologous strains showed significantly higher lung virus titres compared to homologous vaccination, while ponies showed no significant difference in virus excretion titres between groups
- •In both models, the number of animals excreting virus increased with earlier vaccine strain isolation dates (26-year range from 1963–1989), though statistical significance was only achieved in hamsters
- •Both pony and hamster models concluded that heterologous vaccines may be less effective than homologous vaccines at preventing virus excretion despite model differences
- •Hamster model demonstrates potential as a preliminary screening tool for assessing antigenic drift effects on equine influenza vaccine efficacy, though further validation is required