In earlier studies in man it has been demonstrated that
streptomycin-dependent shigellae, if given orally in 5 sufficiently large doses, confer a very high type-specific protection against
bacillary dysentery.In the present study, 2 groups of Erythrocebus patas monkeys were immunized with live
streptomycin-dependent Shigella flexneri 2a, and a third group was not vaccinated. One of the vaccinated groups was given
streptomycin with each dose of the live
vaccine. The animals that received
streptomycin with the
vaccine were shedding these organisms in their faeces for a significantly longer period than the animals that did not receive
streptomycin. A week after the last dose of
vaccine, the animals were challenged with virulent Sh. flexneri 2a organisms. All the control animals developed diarrhoea and excreted challenge organisms for an average of 9 days. None of the 9 immunized animals showed pathological changes nor symptoms of
dysentery. On average, they excreted challenge organisms for only 2.3 days.Immunological tests confirmed the immunity of the vaccinated animals.This study shows that 3 doses of live oral
streptomycin-dependent Shigella
vaccine given together with
streptomycin are at least as effective as immunization with 5 doses of the same
vaccine without
streptomycin. Oral application of
streptomycin, therefore, seems to have had an enhancing effect on the immunizing property of live oral
streptomycin-dependent enteric
vaccines.