Plague has existed in Madagascar since 1896, with epidemic control achieved by GIRARD with an EV vaccine in 1937. Plague persists in Madagascar, however, due to the large animal reservoir. With a predilection for nodal tissues, Yersinia pestis is a virulent bacteria that is potent inducer of antibody synthesis. Immunity mechanisms stimulated by infection were studied: 1. In human by immunoenzymatic methods 2. In mice by seroprotection and vaccinating tests. Induced immunity for people in endemic and endemic-epidemic areas, is significant, affecting approximately 70% of these populations. In non endemic areas, immunity is found in only 33% of the population, perhaps this explains the persistence of epidemic? In all cases, this immunity is a quick onset (6 days), is persistent (> 2 years), and has demonstrable serious recognition of YOP (Yersinia Outer Proteins) by Western Blot method. Human antibodies were shown to be protective for mice. Animals vaccinated by YOP were protected equally well, when compared to animals infected with Yersinia pestis and subsequently treated with antibiotics. Finally, YOP aerosols were also shown to induce antibodies. In conclusion, plague is a vaccinatable bacterial disease and YOP can be used as an animal vaccine to permit plague control in the rat reservoir.