Preliminary results of a large-scale trial of a candidate AIDS vaccine (AIDSVAX®) have been announced by the biotechnology company VaxGen. The trial was a three year, multinational randomized, double-blind placebo controlled Phase III trial of AIDSVAX (rgp120) to prevent HIV infection.

The study did not show a significant reduction of HIV infection as a whole. For the majority of the participants - who were Caucasians - the effect of the vaccine was minimal. The company stressed that the results announced represent findings from an initial analysis and that additional studies will be conducted over the coming weeks to further clarify the data.

The AIDSVAX Phase III trial was the first large-scale human trial of an HIV vaccine. The trial was made possible through the involvement of over 5400 volunteers from the United States, Canada, and the Netherlands, the majority of whom were men who have sex with men. The vaccine used in this trial was designed to reduce susceptibility to infection with HIV subtype B, which is prevalent in the Americas, Western Europe, Australia, and New Zealand. To date, eleven subtypes of HIV-1 have been identified. Thus, one of the major challenges in HIV vaccine development is to develop one or multiple vaccines effective against all major subtypes of HIV.

VaxGen is also conducting another Phase III trial in Thailand, involving a vaccine candidate based on HIV subtypes B and E. That trial, which involves more than 2500 volunteers (mostly injecting drug users) is expected to provide additional information about the potential efficacy of this type of candidate vaccine. Results are expected by late 2003. VaxGen is also currently conducting pre-clinical research to develop a vaccine against the most common subtype, subtype C, which accounts for approximately 50% of all new HIV infections worldwide.

Several other candidate vaccines based on different HIV subtypes are being tested by other public and private organizations, mostly in the United States and Europe, but also increasingly in developing countries, where a total of 22 vaccine candidates have been or are being tested including in Brazil, Haiti, Kenya, Peru, Thailand, Trinidad and Tobago, and Uganda. At least one of these candidate vaccines is expected to enter Phase III trials this year in Thailand, with results available four years later.

References

1. WHO Press Release, 24 February 2003. http://www.who.int/mediacentre/releases

2. VaxGen announces initial results of its Phase III AIDS vaccine trial. http://www.vaxgen.com