Controlled field trial of a high-dose oral killed typhoid vaccine in India.

A controlled field trial of a modified vaccine containing Salmonella typhi, TY 2 strain, in a dose of 400 x 10(9) killed organisms per capsule, was carried out in schoolchildren aged 6-17 years. The children were followed up for 6-8 months. There were 66 cases of typhoid fever in the vaccine group (7312 children) and 54 in the control group (7292 children who had received a placebo). This difference is not statistically significant. The results confirm that, as found in earlier trials, oral typhoid vaccine, in the dosages used so far, gives no protection.