Abstract
A press conference on Thursday September 24 in Bangkok, Thailand, released data that an experimental vaccine provided mild protection against HIV-1 infection. This is the first positive signal of any degree of vaccine efficacy in humans, more than a quarter-century after scientists discovered the virus that causes AIDS. The research was conducted by a team including Thai researchers, the U.S. Army and the U.S. National Institutes of Health. The RV144 Phase III clinical trial, which began in 2003, had been disparaged by many critics as a waste of time and money because each of the two components had been shown to produce no benefit as individual vaccines and because the scientific rationales behind the immunogens were just wrong. It was nevertheless speculated that using them together in the prime-boost scenario could be more effective, with the aim to induce heightened CD4+ cellular immune responses against the viral Envelope protein. This optimism seems to have been validated. In fact, this would not be the first time that the discovery of an effective vaccine relied as much on serendipity as opposed to scientific rationale. On the other hand, many questions remain about the RV144 trial, and these issues will be addressed in this editorial.
Highlights
The limited information provided by the trial sponsors in their press release is that 74 out of 8,198 volunteers who received placebo immunizations became infected with HIV-1 compared to 51 out of 8,917 volunteers who received the prime-boost vaccine
The vaccine had no effect on postinfection viral loads among the recipients who became infected. This 31% value is below the 50% reduction rate defined as "unequivocal clinical benefit", and the margin of error is wide; so it does not suggest that the experimental vaccine should be deployed for general use
The priming vaccine, called ALVAC and made by Sanofi Pasteur in Lyon, France, consists of a version of the canarypox viral vector that was engineered to contain synthetic versions of three HIV-1 genes that encode the Gag and Protease proteins of subtype B and a chimeric form of the Envelope protein
Summary
The limited information provided by the trial sponsors in their press release is that 74 out of 8,198 volunteers who received placebo immunizations became infected with HIV-1 compared to 51 out of 8,917 volunteers who received the prime-boost vaccine. The results equate to a protective efficacy of a little over 31%, with a p value of less than 0.039, just below the widely accepted significance cutoff of 0.05. The vaccine had no effect on postinfection viral loads among the recipients who became infected. This 31% value is below the 50% reduction rate defined as "unequivocal clinical benefit", and the margin of error is wide; so it does not suggest that the experimental vaccine should be deployed for general use. It is enough to justify further research into deciphering the underlying mechanism which provides for the protection observed and - when the results will be sustained during the coming months - putting additional efforts into improving this approach
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