From bbc: http://news.bbc.co.uk/1/hi/health/8272113.stm Trial HIV vaccine cuts infection Developing an HIV vaccine has proved difficult An experimental HIV vaccine has for the first time cut the risk of infection, researchers say. The vaccine - a combination of two earlier experimental vaccines - was given to 16,000 people in Thailand, in the largest ever such vaccine trial. Researchers found that it reduced by nearly a third the risk of contracting HIV, the virus that leads to Aids. It has been hailed as a significant, scientific breakthrough, but a global vaccine is still some way off. The study was carried out by the US army and the Thai government over seven years on volunteers - all HIV-negative men and women aged between 18 and 30 - in some of Thailand's most badly-affected regions. The vaccine was a combination of two older vaccines that on their own had not cut infection rates. Half of the volunteers were given the vaccine, while the other half were given a placebo - and all were given counselling on HIV/Aids prevention. The results found that the chances of catching HIV were 31.2% less for those who had taken the vaccine. "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." The findings were hailed by the World Health Organization (WHO) and the Joint United Nations Programme on HIV/Aids (UN/Aids). They said while the results were "characterised as modestly protective... [they] have instilled new hope in the HIV vaccine research field". Some 33 million people around the world have HIV. Research into a vaccine has been made difficult because HIV is very good at hitting the immune system, the BBC's health correspondent, Jane Dreaper, reports.