[Typhoid vaccination yesterday and today]

Despite the early attempts to produce resistance against typhoid fever with parenteral vaccination by Pfeiffer and Kolle in 1896, and with oral vaccines by Carroll in 1904, it was not until the 1950s when typhoid vaccine efficacy was prospectively evaluated in both well-controlled field trials and human volunteer studies. Among the parenteral whole cell preparations the acetone-inactivated and heat-phenol-killed vaccines, respectively, demonstrating an efficacy of 60-90% for 3-5 years, have received most attention. Oral killed typhoid vaccines have enjoyed popularity for many years, but their effectiveness has never been proven under statistically and epidemiologically controlled conditions. More encouraging results were obtained with live oral vaccines produced from genetically defective, avirulent mutants. Investigations with streptomycin-dependent strains of Salmonella typhi were followed by studies of so-called galE mutants. One of such vaccine strains, labelled Ty 21a, proved to be more effective in volunteer studies than all previous vaccines, and promoted 95% resistance to clinical illness for three years in a field trial in Egypt. It has to be borne in mind, however, that immunity to typhoid fever is never absolute but depends on the dose of infection. This is important to be known by the vaccinee in order to avoid a wrong feeling of security which might result in negligence of personal and food hygiene.