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Survival curves of chickens (n = 8 per group) immunized with two doses of one of the four commercial H5 influenza vaccines, of placebo vaccine containing virus-free allantoic fluid, or of control Ck/C58 H5N3 vaccine (known to be efficacious). After challenge with Ck/Qal-Egypt/1/08 (H5N1) virus, the chickens were observed for 14 d.
