The onset and duration of immunity was assessed in ponies vaccinated in a 2 or 3-dose series with a new canarypox-vectored recombinant vaccine for equine influenza virus (rCP-EIV vaccine) expressing the hemagglutinin genes of influenza H3N8 virus strains A/eq/Kentucky/94 and A/eq/Newmarket/2/93.

Forty-nine equine influenza virus seronegative Welsh Mountain Ponies (1- to 3-yr-old males) were studied. Vaccinated and control ponies were challenged with aerosolized influenza virus A/eq/Sussex/89 (H3N8), representative of the Eurasian lineage of circulating influenza viruses. In trial 1, control ponies and ponies that received rCP-EIV vaccine were challenged 2 wk after completion of the 2-dose primary vaccination program. In trial 2, ponies were challenged 5 mo after 2 doses of rCP-EIV vaccine or 1 yr after the first boosting dose of rCP-EIV vaccine, administered 5 mo after completion of the primary vaccination program. After challenge, ponies were observed daily for clinical signs of influenza and nasal swab specimens were taken to monitor virus excretion.

The challenge reliably produced severe clinical signs consistent with influenza infection in the control ponies, and virus was shed for up to 7 d. The vaccination protocol provided clinical and virologic protection to vaccinate at 2 wk and 5 mo after completion of the primary vaccination program and at 12 mo after the first booster.

Conclusion and Clinical Relevance. rCP-EIV vaccine provided protection of ponies to viral challenge. Of particular importance was the protection at 5 mo after the second dose, indicating that this vaccine closes an immunity gap between the second and third vaccination.

Reference: Minke et al. AJVR 68: 213-219, 2007.