Mean SRH antibody in vaccinated horses measured against (a) Ohio/03, (b) Aboyne/05, and (c) Richmond/07. Error bars represent SEM. Ponies received three doses of vaccine (V1, V2 and V3) and were challenged with live equine influenza virus (Ch). Monovalent = Ohio/03 HA, Trivalent = Ohio/03 HA + Aboyne/05 HA + Bari/05 HA, Control = empty CMV/R vector, NS = needle and syringe, NF = needle-free device.