In this article, the coordinator of the WHO's HIV Vaccine Initiative, Jose Esparza, outlines the steps that need to be taken in order to develop a safe, effective and affordable preventive vaccine.

In addition to overcoming considerable scientific hurdles, the development of a successful vaccine will require that multiple clinical trials take place in parallel, in both developing and industrialised countries.

The article explains the nature of the three different levels of clinical trial that vaccines must undergo before they can be licensed for widespread use, and lists which countries have participated (up to 2001).