FIG. 2.
Survival curves of ducks immunized with the rg-WS/244 H5 influenza vaccine containing different doses of HA protein after challenge with a lethal strain of H5N1 avian influenza A virus. White Pekin ducks were immunized with a single dose of rg-WS/244 H5 influenza vaccine containing 1,000, 200, 40, 8, 1.6, or 0.32 ng of HA protein. As a negative control group, ducks were immunized with a placebo vaccine containing virus-free allantoic fluid. The ducks were observed for 14 days after challenge with Dk/Laos/25/06 (H5N1) virus. Ducks that showed severe symptoms of disease were euthanized, and their deaths were recorded on the following day of observation.