last updated: Friday 25 September 2009, 09:42am

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Hopes for new Aids vaccine

An experimental vaccine lowers the risk of HIV infection by about a third, researchers have found.

The vaccine cut the risk of infection by 32 per cent among 16,000 heterosexual Thai volunteers, US and Thai scientists said.

The unexpected result puzzled researchers, who say they cannot figure out why the drug - a combination of canary pox vaccine and the failed HIV vaccine Aidsvax - is working.

Unusually, people who got the vaccine and who became infected anyway had as much virus in their blood and as much immune system damage as unvaccinated HIV patients. This means it helps prevent infection but does nothing to affect the virus once it is in the body.

Researchers stressed that more trials are needed before a commercial vaccine is developed. They warned the formula may not work in Africa and may not protect homosexual men or injecting drug users.

It was designed specifically to work against two subtypes of HIV which circulate in Thailand and Southeast Asia and in the United States and Europe.

The AIDS virus infects an estimated 33 million people globally and has killed 25 million since it was identified in the 1980s. It affects immune cells called T-cells.

Cocktails of drugs can control the virus but there is no cure. In 2007, Merck & Co ended a trial of its vaccine after it was found not to work, and in 2003, Aidsvax used alone was found to offer no protection.

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