Laboratory tests of typhoid vaccines used in a controlled field study.

In 1954-55, a controlled field trial of two types of typhoid vaccine-alcoholized ("vaccine A") and phenolized ("vaccine F")-prepared in Yugoslavia was carried out in the town and district of Osijek. In an attempt to correlate the protection conferred on man by these vaccines with their potency in laboratory animals, arrangements were made for laboratory tests to be performed jointly by the Central Institute of Hygiene, Zagreb, Yugoslavia; the Lister Institute of Preventive Medicine, Elstree, Herts, England; and the Walter Reed Army Institute of Research (WRAIR), Washington, D.C., USA. In this paper, the results of the WRAIR tests are presented.The potency relationship between vaccine A and vaccine F was found to vary with the type of test performed. According to active-immunization tests in mice, using either mucin or saline challenge, vaccine A was more potent than vaccine F, as it proved also in the passive immunization of mice with saline challenge and in Vi-antibody production in rabbits. As judged by the results of the passive immunization of mice with mucin challenge and of O-antibody production in rabbits, there was, however, no clear-cut difference in potency between the two vaccines. And, as indicated by H-antibody production in rabbits, vaccine F was clearly superior to vaccine A. Since vaccine F was also the more effective in man, the last-mentioned findings are of considerable interest, suggesting that the H antigen may be more, and the Vi antigen less, important in protecting man against typhoid fever than is currently considered to be the case.