A medical trial has revealed what could be the most significant development yet in the search for an effective HIV vaccine.

Researchers in Thailand say the results of a vaccine trial conducted over the past six years are the most promising to date - actually preventing some people from becoming infected with the virus.

But it is still a long way from being a useable vaccine.

For decades researchers have been seeking an effective vaccine for the human immunodeficiency virus, HIV.

The latest study in Thailand involved more than 16,000 healthy men and women aged from 18 to 30.

The trials were conducted in areas of high HIV risk, in the provinces of Chonburi and Rayon, home to the city of Pattaya, Thailand's sleaze capital.

The region is also a hotspot for migration to and from Cambodia.

The trial began in October 2003 and wrapped up just a few months ago.

The results revealed the risk of getting HIV fell by almost a third for those who were vaccinated versus those who were not given the vaccine.

Dr Supachai Rerks-Ngarm from Thailand's Ministry of Public Health says it is not exactly known what makes the so-called prime-boost combination of two vaccines work, but they say it is a breakthrough.

"This is the first project in the world where the design of the vaccine is not only safe, but it can also help reduce the chance of infection. It gives hope that an HIV vaccine can be developed," he said.

'Too low to risk'

This study will be used in further research but Don Baxter from the Australian Federation of AIDS Organisations says it is unlikely that the vaccine will be made available to the general public.

"Well it's the first vaccine that I think that's really shown any efficacy," he said.

"But 30 per cent is far too low to risk putting it out into a general population because condom use would drop and we'd actually end up with more infections."

If an effective vaccine can be developed it would help the estimated 650,000 Thais who have the virus, among them close to 15,000 children.

The trials were funded and assisted by the US Army, which has spent $140 million in this trial alone to ensure that its troops are protected from the infection as they travel the world and to assist in the global fight against the virus.

The United States Ambassador to Thailand, Eric G John, says the trial brings scientists closer to finding an effective vaccine for the virus.

"This trial will be recognised as a testament to Thailand's ability to successfully execute a complicated vaccine trial, the largest ever attempted that ended with a credible conclusion and that brought us one step closer to an HIV vaccine," he said.

The United Nations has welcomed the results, saying they offer new hope to the estimated 40 million people worldwide who have contracted the virus.

Source: http://www.abc.net.au/news/stories/2009/09/24/2695951.htm