Field trials with killed oral typhoid vaccines.

The article gives the results of the use of two types of killed oral typhus vaccine administered to students 10 to 19 years of age in two urban areas of the Province of Santiago. Vaccine from the German Democratic Republic (GDR) was administered to 37,517 students and placebo to an equivalent control group. The period of observation was 18 months (November 1973-April 1975). The other product, from the German Federal Republic (GFR) was administered to 37,566 students, with placebo given to an equivalent control group. In this case the observation period was 7 months (October 1974-April 1975). The antigenic composition of the two vaccines is qualitatively and quantitatively different as are the characteristics of their preparation. In the field trial with the product from the GDR, the morbidity for typhoid fever in the vaccinated and control groups showed statistically significant differences, even though on the border line level. Satisfactory and highly significant results had been obtained with the product in earlier field trials. The difference observed between morbidity in the two groups in the field trial with GFR vaccine was not significant. It is emphasized in this regard that the observation period was shorter in this case, which precludes definitive conclusions. A high proportion of reliable confirmation of diagnosis of cases is evident for both field trials. The findings show the need for subjecting this type of vaccine to further and better field trials.