In an early-morning announcement today, researchers reported that an experimental HIV (human immunodeficiency virus) vaccine effectively reduced the number of people who contracted the virus by nearly a third.

Tested in a U.S.-sponsored trial that involved more than 16,000 volunteers in Thailand, the vaccine was administered in six injected doses starting in 2006 to half of the group, and the other half received a placebo. Seventy-four people in the placebo group had contracted HIV by the end of the trial, whereas only 51 of the vaccinated group tested positive.* The injections consisted of two vaccines that had proven unsuccessful on their own: Sanofi-Aventis SA's ALVAC and VaxGen Inc.'s AIDSVAX.

The results came as a surprise to HIV-vaccine skeptics in the AIDS (acquired immunodeficiency syndrome) research field, whose numbers have increased after years of failed vaccine trials. "It's safe to say that the scientific community is caught off-guard," Mitchell Warren, director of the AIDS Vaccine Advocacy Coalition, told Bloomberg News. Before the announcement, Marie-Paule Kieny, director of the World Health Organization's Initiative for Vaccine Research, told the news service: "I don't think that there is a lot of expectation that the efficacy of this vaccine will be very high." A 2007 clinical trial of a vaccine made by Merck was stopped when researchers found that, in fact, more people who received the active vaccine (49) than the placebo (33) had contracted HIV.

Although the news was welcomed by many, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID), noted in a press briefing that the findings should be treated with due temperance. "It's opened up a door for us to ask some very important fundamental science questions as well as some clinical questions," he said at the briefing, The Wall Street Journal reported.

The vaccine was targeted especially toward the virus strain circulating in Thailand, and it may not show the same effectiveness where the virus is different, such as Africa or the U.S. And even the 31.2 percent fewer cases that it resulted in is hardly an ideal preventative strategy. Companies prefer to hedge their bets on vaccines that show at least a 70 percent effectiveness rate, Fauci noted at the briefing.  Others worry that news about the vaccine might lead some to be less vigilant about more proven methods of prevention, such as using condoms.

The results, however, still show progress in a difficult field. "If you have a product that's even a little bit protective, you want to look at the blood samples and figure out what particular response was effective and direct research from there," Fauci said at the briefing, The New York Times reported. More studies will be required to see if the vaccine can be made more effective and translated to other strains of the virus.

In the meantime, Fauci said at the briefing, "It's like we were groping down an unlit path, and a door has been opened," the Times reported.

Image courtesy of iStockphoto/_maximus_

*Note (9/24/09): This sentence has been changed since posting to correct an error.