Equine influenza vaccine containing older H3N8 strains offers protection against A/eq/South Africa/4/03 (H3N8) strain in a short-term vaccine efficacy study.
Authors: Daly J M, Sindle T, Tearle J, Barquero N, Newton J R, Corning S
Journal: Equine veterinary journal
Summary
# Editorial Summary Antigenic drift in equine influenza H3N8 viruses means field strains often diverge significantly from vaccine components, raising questions about cross-protection when novel variants emerge. Daly and colleagues challenged this concern by vaccinating ponies with Duvaxyn IE-T Plus (containing older H3N8 strains) and exposing them to the evolutionarily distant South Africa/4/03 strain two weeks after completing a primary two-dose course, comparing clinical and virological outcomes against unvaccinated controls. Despite antigenic mismatch, vaccinated animals demonstrated both statistically significant reductions in clinical disease scores and substantially lower viral shedding following experimental infection. The findings suggest that existing vaccines can provide meaningful heterologous protection when adequate antibody titres are generated, a particularly pertinent observation for outbreak situations where rapid revaccination might limit transmission even before strain-matched vaccines become available. For practitioners, this supports the use of booster vaccinations during influenza outbreaks as a pragmatic interim measure to reduce disease severity and shedding, though this short-term efficacy study does not clarify whether protection persists beyond the two-week post-vaccination window or whether repeated boosters would prove as effective.
Read the full abstract on PubMed
Practical Takeaways
- •Even when field strains don't perfectly match vaccine composition, existing vaccines can still provide meaningful clinical protection and reduce disease severity in vaccinated horses
- •Vaccinating during an outbreak with currently available vaccines may be beneficial, particularly if high antibody levels can be achieved prior to exposure
- •Booster vaccinations with standard vaccines appear worthwhile when new variant strains emerge, as they can limit infection through cross-protective immunity
Key Findings
- •Duvaxyn IE-T Plus vaccine provided statistically significantly decreased clinical scores in vaccinated ponies after challenge with A/eq/South Africa/4/03 (H3N8) strain
- •Virus shedding was significantly lower in vaccinated ponies compared to unvaccinated controls following challenge infection
- •All vaccinated ponies developed high antibody levels to both vaccine strains (Newmarket/1/93, Newmarket/2/93) and the variant challenge strain (South Africa/4/03)
- •Cross-protection was demonstrated 2 weeks after completion of a 2-dose primary vaccination course with 4-week interval between doses