The Response of Man to Virulent Shigella flexneri 2a

In the United States, epidemic shigellosis has been a particularly important problem in confined groups such as the military, institutions for the mentally retarded, and Indian reservations. It is in such confined populations that an effective Shigella vaccine would be most beneficial. Shigella flexneri 2a is an important cause of both sporadic and epidemic shigellosis in the United States. Between the years 1963 and 1966 this pathogen accounted for approximately one-fourth of all Shigella isolates reported to the National Communicable Disease Center [1]. In 1967 this center recorded 11,405 isolations of all Shigella [2]. In order to test the effectiveness of oral attenuated living S. flexneri 2a vaccines, an experimental model has been developed in man. The response of volunteers to oral challenge by virulent S. flexneri 2a was determined at doses of 104 -108 viable organisms.