This feature article presents the progress and pitfalls made in HIV vaccine research up to May 2002 (before the company VaxGen announced the results of the first large-scale trial of an HIV vaccine in February 2003; as widely reported, and anticipated by this article, the VaxGen trial proved disappointing).

The article describes the scepticism some scientists had about the VaxGen vaccine design, and other strategies now underway.  But although many different vaccines are now in clinical trials, several hurdles remain, including a lack of understanding about what is needed in order to protect against infection, and the rapid mutation and 'escape' of the virus from immune attack. Also uncertain is the extent to which geographical variation in HIV strains – known as clades – are likely to help or hinder vaccine development.