Vaxgen announces second phase III trial failure in its AIDSVAX programme

This article is more than 20 years old. Click here for more recent articles on this topic

The US vaccine developer VaxGen today announced that a phase III study of AIDSVAX adapted for Thailand has failed to show that the vaccine protected against HIV infection during three years of follow-up.

2,546 injecting drug users were randomised to receive either the AIDSVAX product, which is designed to protect against HIV-1 subtypes E and B, or a placebo. The same proportion of people became infected with HIV in the AIDSVAX group and the placebo group (3.1% per year).

Earlier this year VaxGen announced the results of a phase III study using a subtype B HIV vaccine in the United States. That study showed no protective effect in the overall study population, but a suggestion that the vaccine might protect African-Americans and Asians.



In HIV, different strains which can be grouped according to their genes. HIV-1 is classified into three ‘groups,’ M, N, and O. Most HIV-1 is in group M which is further divided into subtypes, A, B, C and D etc. Subtype B is most common in Europe and North America, whilst A, C and D are most important worldwide.


A pill or liquid which looks and tastes exactly like a real drug, but contains no active substance.


A glycoprotein on the HIV envelope. gp120 binds to a CD4 receptor on a host cell, such as a CD4 T lymphocyte (CD4 cell). This starts the process by which HIV fuses its viral membrane with the host cell membrane and enters the host cell.

phase III

The third and most definitive stage in the clinical evaluation of a new drug or intervention, typically a randomised control trial with the new intervention compared to an existing therapy or a placebo, in large numbers of participants (typically hundreds or thousands). Trial results are used to evaluate the overall risks and benefits of the drug and provide the information needed for regulatory approval.

statistical significance

Statistical tests are used to judge whether the results of a study could be due to chance and would not be confirmed if the study was repeated. If result is probably not due to chance, the results are ‘statistically significant’. 

The company was widely criticised for its interpretation of the results, and when statistical experts from the US National Institutes of Health and other institutions carried out further analyses, they found that the apparent protective effect may have been an effect of the way in which the analysis was carried out. They found that the chance of finding a statistically significant result within a subgroup increased as the number of analysed subgroups rose. The NIH-led panel concluded that the result was “likely to be spurious” (for further information about this debate, see the recent report in TAGline, the newsletter of the Treatment Action Group).

The results of VaxGen’s Thai study are likely to undermine further interest in vaccine regimens that include gp120 (the HIV protein used in the AIDSVAX), including a proposed NIH study of a gp120 vaccine used as a booster after a canary pox-based vaccine (designed to elicit cellular immune responses to HIV).

Further information on this website

Preventive vaccines against HIV infection

Recombinant sub-unit vaccines (the class of vaccines that includes AIDSVAX