Failure of Aids trial casts doubt on hopes for cure

Hopes of developing a vaccine to protect future generations against Aids suffered a setback yesterday when the first clinical trial to complete its final stage ended in failure.

American scientists struggled to conceal their disappointment at the results of the three-year study on 5,000 men and women at high risk of the disease. The vaccine on trial cut the HIV infection rate by just 3.8 per cent. They pinned their hopes on the much greater effect of the vaccine among the 500 blacks and Asians in the trial where there was a 67 per cent reduction in the infection rate. But they warned that those numbers were too small to be sure the effect was real.

"Overall what we see is the trial failed," said Donald Francis, president of Vaxgen, manufacturer of the vaccine. But he added that there was a group of 500 people where there had been "clear efficacy". "The challenge here is to see if this is a statistical fluke," he said. Half of all American cases of HIV are among blacks and across the world 80 per cent of sufferers are black. The vaccine, known as Aidsvax, was formulated to protect against the B strain of the virus, which is prevalent in North America and western Europe.

Neil Flynn, professor of medicine at the University of California and one of the principal researchers, said early indications suggested blacks developed a stronger antibody response to the vaccine and thus developed better protection, probably because of their different genetic make-up. "They are the hardest group to hit on Earth. That is hopeful," he said. "These results suggest the people who need it [the vaccine] most get the best response."

About 30 Aids vaccines are being developed to protect against the disease, which has killed 28 million people worldwide and left 40 million HIV positive. Aidsvax was the first to complete phase three clinical trials, testing its efficacy in humans, and the results are a bitter blow to hopes of stemming the global epidemic

The researchers had been looking for at least a 30 per cent overall reduction in infections to satisfy the US Food and Drug Administration (FDA) and allow further trials to go ahead. Whether the 67 per cent reduction among the small group of blacks and Asians would be sufficient to persuade the FDA was not immediately clear. It has never previously approved a vaccine based on its efficacy in a minority group.

The trial was launched in 1998 in America, Canada, Puerto Rico and the Netherlands. Most of the participants were homosexual men but they included 300 women at high risk (with an HIV partner, for example). Each participant had at least three injections.

Of the 498 blacks and Asians, 171 were given placebo injections and of these 17 were infected with HIV, a 10 per cent rate. Of the 327 given the vaccine 12 were infected with HIV, a rate of 3.7 per cent, or 67 per cent below the placebo group.

Among the 4,511 whites, 1,508 were given a placebo of whom 81 were infected, a rate of 5.4 per cent. Among the 3003 given the vaccine, 179 were infected, a rate of 6 per cent.

One fear had been that vaccinating people would give them a false sense of security but a study by the US Centers for Disease Control and Prevention found trial participants reduced risky behaviour.

Vaxgen is nearing the end of a second phase three in Thailand. The results will be released later this year. That vaccine is designed to protect against HIV strains more commonly seen in Asia.