Strategies aiming to eradicate the poliovirus and poliomyelitis seek primarily to eliminate wild strains associated with the disease, by means of world wide vaccination campaigns using the oral attenuated vaccine (OPV). OPV contains attenuated viral strains which retain their replicating capacity in the digestive tract and thus induce the development of an antiviral local intestinal immunity and limit the circulation of the virus. In such a context, poliomyelitis surveillance laboratories should study above all cases of acute flaccid paralysis (AFP), highlighting the circulation of wild strains, identifying regional reservoirs and guiding vaccination strategies. Alongside circulation, there appear to be important genetic and phenotypic shifts in vaccinating strains, since the OPV is capable of preserving a reservoir of pathogenic stains and thereby impairing vaccination efficacy and the eradication of the virus. Furthermore, non-polio enteroviruses should be considered as a source of emerging pathogenic strains. These questions are being studied by the Pasteur Institute with the objective of determining the effects of OPV campaigns on the circulation of the poliovirus. We have studied the poliovirus vaccine and the circulation of wild strains in urban and peripheral urban areas in African countries known to be endemic for poliomyelitis (Central African Republic, Madagascar, Côte d'Ivoire). The study population consisted of children who had already been vaccinated and new-borns in the course of vaccination. We also evaluated the diffusion of the vaccine strains in their immediate environment. Genetic interchanges were taken into account. For children who received the 3-4 OPV doses, asymptomatic virus excretion was insignificant (0.4-2.4%). The rate of virus excretion in the surrounding environment of children in the course of being vaccinated was relatively low (1.76-5.3%). Our study also detected variant and recombinant strains.