A controlled field trial of liver oral typhoid vaccine Ty21a.

A controlled field trial of a live oral typhoid vaccine was carried out in Alexandria, Egypt, in 1978-79. A total of 32 388 children were included in the study. They were divided in two comparable groups, one given 3 doses of the vaccine and the other 3 doses of the placebo. Each active dose contained 1 x 10(9)-8 x 10(9) live Ty21a bacteria. From March 1978 to March 1979, the population studied was followed up and suspected typhoid cases were investigated bacteriologically and serologically. The effectiveness of the vaccine was assessed by analysis of the incidence of typhoid fever in the two groups. The results of the follow-up indicate that, in the dosage schedule used, the Ty21a mutant strain, found previously to be stable and safe, is protective against typhoid fever for at least one year.