Protection rate of freshly prepared, 3- and 6-months stored different vaccines after single-dose administration. Results were the average of duplicate trials in a single experiment (mean ± SEM). Bars with different letters in the same group represent a significant difference (p< 0.05). 1,2: Alum gel-based vaccine with 108 and 109 CFU/0.5 ml/dose, respectively, 3,4: Montanide oil-based vaccine with 108 and 109 CFU/0.5 ml/dose, respectively, 5,6: commercial vaccine A and B, respectively, 7: control positive and 8: control negative.