Limited success for AIDS vaccine but there is hope for some ethnic groups
Vaxgen has reported a low overall success rate for its vaccine, Aidsvax, in a study designed to test how well the vaccine prevents HIV infection. Black and Asian subgroups, however, showed a better response than the study population as a whole.
The reduction of infection among the entire sample of volunteers, including all racial groups, was just under 4 per cent — not statistically significant. However, there were 67 per cent fewer HIV infections among ethnic minorities, other than Hispanic individuals, compared with placebo recipients (P<0.01). Among black volunteers there were 78 per cent fewer infections compared with placebo (P<0.02). Protection appeared to correlate with higher levels of vaccine-induced neutralising antibodies.
VaxGen says that it does not know why response might be different in these groups but adds that it intends to conduct additional analyses to confirm the findings. It points out that subgroup numbers were small and that infection rate among ethnic groups was not a primary endpoint for the trial.
A company statement says: "With regard to ethnic minorities in the trial, there is less than a 1 per cent possibility that the observed difference in infection rates could have occurred by chance. There is less than a 2 per cent possibility that the observed difference in infection rates among black volunteers could have occurred by chance."
The company's chief executive, Lance Gordon, said that VaxGen intends to continue development of this vaccine, carrying out further studies in subgroups. In parallel it will continue work to make the product more broadly effective. The company is discussing its results with the United States Centers for Disease Control.
A spokesman for the Terrence Higgins Trust told The Journal that although the results were disappointing, there were 30 other trials of HIV vaccines being conducted. "These results remind us just how difficult developing a vaccine against HIV is because of the nature of the virus," he said.
The randomised, double-blind, placebo-controlled phase three trial involved 5,108 men who had sex with men, and 309 at-risk women, all of whom were meant to be HIV negative when they were recruited. During the 36-month study, conducted in the United States, Canada, Puerto Rico and the Netherlands, a total of seven injections were administered at months 0, 1, 6, 12, 18, 24 and 30.
Volunteers received regular counselling to avoid risks that could lead to HIV infection. Preliminary analysis indicated that risk behaviour was reduced in both the placebo and vaccine groups.
Aidsvax is composed of a recombinant form of gp120, a protein found on the surface of HIV. The engineered protein mimics antigens on the surface of two strains of HIV subtype B, which is prevalent in North America, Europe, Australia, Japan and Puerto Rico.
Citation: The Pharmaceutical Journal URI: 11096262