Live attenuated RNA viruses make highly efficient vaccines. Among them, measles virus (MV) vaccine has been given to a very large number of children and shown to be highly effective and safe. MV vaccine induces a life-long immunity after a single or two low-dose injections. It is easily produced on a large scale in most countries and can be distributed at low cost. Reversion to pathogenicity has never been observed with this vaccine. Because of all these characteristics, MV vaccine might be a very promising vector to immunise children against both measles and other infectious agents, such as HIV or flaviviruses, in the developing world. In this article, we describe recent data that we obtained showing the capacity of recombinant Schwarz MVs to express proteins from human immunodeficiency or West Nile viruses, and to induce specific immune responses able, in the case of West Nile virus, to protect from an experimental challenge.