For the first time, scientists say an investigational vaccine has modest potential for protecting people against HIV infection, the Associated Press reports. “The vaccine — a combination of two previously unsuccessful vaccines — cut the risk of becoming infected with HIV by … 31 percent in the world’s largest [HIV] vaccine trial of more than 16,000 volunteers in Thailand, researchers announced Thursday in Bangkok,” the news service writes (Marchione/Casey, 9/24).

“‘It’s the first evidence that we could have a safe and effective preventive vaccine,’ Colonel Jerome Kim of the U.S. Army,” which sponsored the trial, said at a press conference, the Financial Times reports, adding, “Doctors said an actual vaccine was still some way away but the tests provided a valuable ‘proof of concept'” (Johnston, 9/24). Other supporters of the trial include the National Institute of Allergy and Infectious Diseases (NIAID), the Thai Ministry of Public Health “and the patent-holders in the two parts of the vaccine, Sanofi-Pasteur and Global Solutions for Infectious Diseases,” the New York Times reports (McNeil, 9/24).

For the study, “[t]he researchers enrolled volunteers in Thailand’s Chon Buri and Rayong provinces, which have the nation’s highest rates of HIV, according to the study Web site,” Bloomberg writes. “Subjects were given four doses of the ALVAC vaccine [made by Sanofi-Pasteur] and two of the AIDSVAX shot [made by VaxGen, now owned by Global Solutions for Infectious Diseases] over six months, then monitored for three years. They were also given advice on safe sex” (Bennett, 9/24).

The New York Times adds: Approximately “half the 16,402 volunteers were given six doses of two vaccines in 2006 and half were given placebos. Of those who got placebos, 74 became infected, while only 51 of those who got the vaccines did” (9/24).

“The results were barely significant on statistical grounds, perplexing for scientific reasons and unanticipated by most researchers,” the Washington Post writes. “Nevertheless, the first positive results for an [HIV] vaccine after two decades of experimentation was being called a milestone” (Brown, 9/24).

Bloomberg continues: “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 viral load (9/24).

“‘The study results, representing a significant scientific advance, are the first demonstration that a vaccine can prevent HIV infection in a general adult population and are of great importance,’ the Geneva-based World Health Organisation and the Joint United Nations Programme on HIV/AIDS (UNAIDS) said” in a statement, Reuters writes. “It remains to be seen if the two specific vaccine components in this particular regime would be applicable to other parts of the world with diverse host genetic backgrounds and different HIV subtypes driving different regional sub-epidemics,” according to the WHO and UNAIDS, Reuters reports (Nebehay, 9/24).

The Telegraph writes, “The researchers have been careful to say the vaccine combination appears to have an effect on the HIV strain circulating in Thailand and it may not work on other strains elsewhere in the world” (Smith/Jamieson, 9/24).

The Washington Post includes comments by Anthony Fauci, director of NIAID, who said, “Conceptually, we now know a vaccine is possible. Whether the vaccine is going to look anything like this one I don’t know. But at least we know it can be done” (9/24). The New York Times reports, “Fauci said that scientists would seldom consider licensing a vaccine less than 70 or 80 percent effective, but he added, ‘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'” (9/24). A NIAID press release is available here (9/24).

“Mass-producing the vaccine, plus how to proceed with future studies, will be discussed among the governments, study sponsors and companies involved in the trial, Kim said. Scientists want to know how long protection will last, whether booster shots will be needed, and whether the vaccine helps prevent infection in gay men and injection drug users, since it was tested mostly in heterosexuals in the Thai trial,” the AP reports (9/24).

BBC reports, “‘This result is tantalisingly encouraging. The numbers are small and the difference may have been due to chance, but this finding is the first positive news in the AIDS vaccine field for a decade,’ said Dr. Richard Horton, editor of the Lancet medical journal. ‘We should be cautious, but hopeful. The discovery needs urgent replication and investigation'” (9/24). BERMANA.com reports that the study “will form an important foundation for further HIV vaccine development in Thailand in the future,” Paijit Warachit, deputy health permanent secretary in Thailand, said (9/24).

The Washington Post adds: “Many details of the trial were not released Wednesday afternoon in briefings to reporters,” leading some to some skepticism among health experts. “More information will be presented at an AIDS vaccine meeting in Paris later this fall” (9/24).

Science’s blog, “Science Insider,” also reports on some researchers’ skepticism over the results of the clinical trial (Cohen, 9/24).