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Immunity in shigellosis. II. Protection induced by oral live vaccine or primary infection.

Two attenuated strains of Shigella flexneri 2a, a Shigella-E. coli hybrid, and a streptomycin-dependent mutant, were safely given to adult male volunteers. When vaccinated individuals ingested virulent S. flexneri 2a, clinical disease and fecal excretion of virulent organisms occurred with less frequency than in unvaccinated volunteers. The level of immunity resembled that seen after recovery from active infection. These studies have given some indication that bacillary dysentery may be controlled by an oral live vaccine, and field trials designed to quantitate induced immunity are planned for the near future.