Mean serum IgG antibody titres to capsular polysaccharide of C. jejuni strain 81-176. Serum antibody titres were determined by ELISA. Error bars represent the standard error of the mean. At no point in time did the titres differ significantly among the experimental groups (Kruskal–Wallis nonparametric test). By the day of necropsy (day 38, 9 days post-challenge) 33% of vaccinated birds and 0% of PBS placebo birds had seroconverted with a four-fold or greater increase in antibody titre (≥2 log2 units), (see Figure 3).