Fig. 3

Serum titres of HA1–2-specific IgG. Specific pathogen-free chickens (n = 8) were vaccinated intramuscularly with three doses of candidate vaccines. Chickens were subjected to bleeding in 12 days after the second and third immunisations. Serum IgG titres were measured via enzyme-linked immunosorbent assay. Data are presented as the mean ± standard error of the mean. Statistical significance of differences is illustrated as follows: *P < 0.05, **P < 0.01