Protection rate of different vaccines against A. paragallinarum after single and booster dose administration. Results were the average of duplicate trials in a single experiment (mean ± SEM). * Represents the significant differences between single and booster dose administration, * p < 0.05, ** p < 0.01, *** p < 0.001, ns: no significance. 1,2,3: Alum gel-based vaccine with 107, 108 and 109 CFU/0.5 ml/dose, respectively, 4,5,6: Montanide oil-based vaccine with 107, 108 and 109 CFU/0.5 ml/dose, respectively, 7, 8: commercial vaccine A and B, respectively, 9: control positive and 10: control negative.