Among the large amount of likely hazards in the South West of the Indian Ocean region (hurricanes, torrential rains, tsunamis, infectious diseases …), some are more devastating and present than others. The Chikungunya epidemic that lasted from 2004 to 2006, as probably the major public health event, has left a strong impact on men, societies, and people’s mind. This epidemic hit the states and territories in the region with 25% up to 60% prevalences. In an attempt to characterize the outlines of vulnerability and to determine contextual effects, we conducted an analysis of levels in human, social and health development in the involved countries. Although it has been established emergence factors on a regional scale are nevertheless widely related to social-spatial variables, and given equal hazard, the risk is not proportionally more important than in the known most vulnerable countries. On the scale of La Reunion, a data analysis of the social-spacial and epidemiologic environment with nearly 3000 cases georeferenced during the first phase of the epidemic, allows to assess the main areas at risk on the island.