The long search for an AIDS vaccine has produced countless false starts and repeated failed trials, casting once bright hopes into shadows of disenchantment. The now familiar swings appeared in high relief this past fall, with news of the most recent, phase III trial in Thailand. Initial fanfare for a protective outcome gave way to disappointment after reanalysis showed that the protection could be attributed only to chance. But rather than dashing all hopes for an AIDS vaccine, the trial has heartened some researchers, who see new clues in the battle against the fatal illness.
Costing $150 million and enrolling more than 16,000 subjects, the Thai clinical trial was the largest AIDS vaccine test to date. It began in 2003, and early results released in September showed a slim but statistically sound benefit from the vaccine (a series of inoculations with drugs known as ALVAC-HIV and AIDSVAX B/E). But in October the full report, with various statistical analyses, was released in a Paris meeting to greater skepticism. Specifically, 74 people who had received the placebo became infected with HIV in the trial period, compared with the 51 people who became infected after receiving the vaccine, which makes for a protective effect of 31.2 percent. By including, however, the seven people who turned out to have had HIV at the start of the trial (two in the placebo group and five in the vaccine group), the effectiveness drops to 26.4 percent.