A large human trial for the AIDS vaccine in Thailand has, for the first time, prevented HIV from spreading in 31.2% of those vaccinated
An experimental vaccine has for the first time prevented HIV infections, a breakthrough that has eluded scientists for a quarter century.
A huge US-funded study involving more than 16,000 volunteers in Thailand found that a combination of ALVAC, made by Paris-based Sanofi-Aventis SA, and AIDSVAX, from VaxGen Inc, of south San Francisco, cut infections by 31.2% in people who received it, compared with those on a placebo.
Neither vaccine had stopped the virus that causes AIDS when tested separately in previous studies, but the two-pronged attack has had partial success.
“This is the first concrete evidence since the discovery of the virus in 1983 that a vaccine against HIV is eventually feasible,” Michel DeWilde, senior vice-president of research at Sanofi Pasteur, the French drug maker’s vaccine arm, said in a statement.
Researchers enrolled volunteers in Thailand’s Chon Buriand Rayong provinces which have the nation’s highest rates of HIV. Subjects were given four doses of the ALVAC vaccine and two of the AIDSVAX shot over six months, then monitored for three years. They were also given advice on safe sex. There were no serious side effects, the researchers said.
Of those who received the vaccine, 51 became infected with HIV compared with 74 who received a placebo, the researchers said. Those in the study who became infected with HIV during the trial were given free access to treatment.
In another finding, the vaccine failed to reduce the amount of virus in the blood of subjects who became infected. Researchers had hoped that if the vaccine didn’t prevent infections, it would at least cut the virus to levels so low it couldn’t be transmitted. The researchers don’t understand exactly how the vaccine prevented infections or why it didn’t reduce the viral load.
“Although the results were modest, with an efficacy of 31.2%, this is a very important scientific advance, and gives us hope that a globally effective HIV vaccine may be possible in the future,” said Jerome Kim, deputy director of science at the Walter Reed Army Institute of Research, which sponsored the trial.
Critics of the study, which cost $105 million, are more cautious about accepting the results.
“Wow!” said AIDS vaccine researcher Ronald Desrosiers, head of the New England Primate Research Centre in Southborough, Massachusetts. “Looking at the numbers, it’s underwhelming to me. But I want to sit tight and get a bunch of people to do analyses and see whether the protective effect holds up under greater scrutiny.”
Dennis Burton, an immunologist at the Scripps Research Institute in San Diego, California, had a similar reaction. “It’s very early days,” he said. “People should be enormously cautious now.” In an editorial published in Science (January 16, 2004, p 316), shortly after the trial began, Desrosiers, Burton, and 20 other prominent AIDS researchers argued that the study never should have been launched.
Scepticism about the study stemmed from previous lacklustre results of the vaccines, tested separately and together, in smaller clinical trials. In the just-finished trial, vaccinated individuals first received “priming” from a preparation, made by Sanofi Pasteur, that contained a canarypox virus that researchers had engineered to contain HIV genes. A “booster” shot contained a recombinant form of HIV’s surface protein, gp120, made by VaxGen. VaxGen sold the rights to develop the product to Global Solutions for Infectious Diseases after the product failed in large efficacy trials when tested alone.
Even though the data is positive, US military researchers stress that many discussions must still take place before anyone decides to use vaccines with such modest efficacy. Still, Colonel Nelson Michael, director of the US Military HIV Research Programme, said he hopes the results will help researchers finally untangle which immune responses correlate with protection, and then build on that information to design more effective vaccines. “These results at least are telling us that walking down this road is worthwhile,” he said.
Source: AIDS-INDIA, September 24, 2009
