Sixteen thousand people volunteered for the study—
primarily Thai sex workers and IV drug users from the general population of two Thai provinces. All received condoms, HIV prevention counseling, and an offer for HAART therapy if they became positive. Eight thousand received a placebo shot, the other half six doses of two distinct (and previously failed) HIV vaccines. About five years later, 74 of the placebo recipients were newly HIV positive. Twenty-three fewer, 51 total, among the vaccine recipients were now HIV positive. It was a statistically significant reduction in infection among the vaccinated.
After years of struggle, and some truly distressing failures, this is the one and only successful HIV vaccine trial.
It definitely was an odd approach. Take two failed vaccines, combine them together, and see if they'll work. The first vaccine stuffed into a tamed Canarypox virus some of the critical functional proteins of the HIV virus. (Canarypox is in the same broad family of viruses that includes Smallpox. Birds are the desired home of Canarypox; it's capable of getting into human cells, but not properly replicating itself once in. As such, it has the ideal vaccine combination of really pissing off the human immune system while being incapable of causing injury.) The second, booster, vaccine was simply some of the purified and isolated surface protein (gp120) from the HIV virus. (This booster vaccine is a bit like going around the human immune system with a mugshot of the HIV virus. The isolated protein is incapable of causing disease, but gives the whiff of what the real deal is like.) When the study was first proposed, parts of the scientific community were non-plussed. Isn't zero times zero still zero?
Nope, it's one third. What do you do with a vaccine that only works sometimes, or only for some? For a vaccine to be considered clinically useful (i.e, after the shots are done, you can feel confident in telling someone they are vaccinated and protected against the infection), you'd hope to have at least 70-80% of those vaccinated to be protected. (Herd immunity takes care of the rest of the risk, eventually.) Further, this vaccine combination (bizarrely) failed to produce neutralizing antibodies even in the successfully vaccinated.
For the next few months and years, the results of this study will be torn into, trying to answer some of these questions. In the meantime, this is an extremely heartening sign—indicating a real potential to salvage other failed vaccines into successful combination therapies.