[A comparison of the serological effects of classical cholera vaccine and of purified fraction vaccine, with or without simultaneous yellow fever vaccine (author's transl)].

In order to test whether simultaneously administered cholera vaccine has a depressive effect on yellow fever vaccine, a controlled trial was undertaken on school-age children in the South-Central Province of Cameroun. In addition to this principle objective, the study also permitted a comparison of the serological response in subjects vaccinated with classical cholera vaccine and in those vaccinated with a purified fraction vaccine, either with or without simultaneous yellow fever vaccine. The evaluation was measured by changes in vibriocidal antibodies and cholera agglutinins 30 days after vaccination. Only subjects without cholera antibodies prior to the study, were included. 1) Results obtained by assay of vibriocidal antibodies. It was confirmed that, no matter which cholera vaccine was used, the simultaneous administration of yellow fever vaccine had no influence on the percentage of subjects showing a significant rise in vibriocidal antibodies (4-fold increase in titre) following vaccination. In addition, in this study the purified fraction vaccine resulted in a significantly higher rate of seroconversion than did the classical vaccine. However, in comparison to other studies using classical cholera vaccine, our figures for seroconversion after purified fraction vaccine show very little, if any, differences. 2) Results obtained by assay of agglutinating antibodies. When measured by this method, there was a high frequency of non-reactors to the vaccines. This may be attributed to the date of the post vaccination blood speciment (30th day after vaccination). It has been shown that agglutinins decay rapidly after the 15th day following clinical cholera. Thus, the late date of the second speciment after vaccination could explain why we were unable to show any difference in the level of agglutinin after either classical or purified cholera vaccination. The simultaneous administration of the yellow fever vaccine did not influence the titre of agglutinins induced by the classic cholera vaccine. On the other hand, using the association, the seroconversion rate as observed on the 30th day post vaccination was significantly higher than that observed when the fraction was administered alone. If one accepts the generally admitted specificity of the agglutination reaction after clinical disease, two hypotheses can be considered: a) the yellow fever vaccine has an adjuvant effect for the production of antibodies induced by the purified fraction vaccine, or b) the addition of yellow fever vaccine has a retarding effect on the elimination of the agglutinins which, in the natural disease, are rapidly eliminated. Further studies to verify these hypothesis should be undertaken.