Big blow: Researchers have found that two 'miracle' AIDS cures not only failed to work but can actually increase people's chances of contracting the virus
It is a massive blow to Aids research, which has ground to a halt - with seven other trials of similarly designed would-be vaccines either suspended or called off indefinitely.
The US government alone pumps £250million a year into research to try to find a "Holy Grail" vaccine which would put an end to Aids.
Now scientists fear the disastrous outcome of the two most promising trials leaves them back at square one.
Hailed as major breakthroughs when the tests began, the US-funded STEP and Phambili studies were shut down when it became clear the vaccines could leave patients more susceptible to the virus, which attacks the immune system and which killed more than two million victims last year - 320,000 of them children.
More than 25million people have died from Aids since 1981 and an estimated 33million are living with the disease, most in Africa.
In the UK, there have been at least 17,600 Aids-linked deaths and more than 88,000 people have contracted the HIV virus which leads to Aids.
The two aborted studies used the same vaccine, made from a common respiratory virus loaded with fragments of HIV.
The STEP study involved male homosexuals in North and South America, the Caribbean and Australia.
The Phambili trial, involving more than 3,000 men and women heterosexual volunteers in South Africa, was halted less than one year into its four-year schedule after it, too, raised fears that the vaccine could endanger patients.
The vaccine was supposed to cut the numberof infections and make the HIV virus less deadly and less contagious in those who had already contracted it.
But, rather than protect the immune system, the tests appeared to show that the vaccine somehow primed it to become more susceptible to HIV.
Results from both trials, which cost about £16million, suggested that people were twice as likely to become infected after having the vaccine.
The debacle has sent shockwaves through Aids organisations that have raised millions of pounds towards research over the past 20 years.
"This is on the same level of catastrophe as the Challenger disaster that destroyed a Nasa space shuttle," said Robert Gallo, co-discoverer of the HIV virus and head of the Institute for Human Virology in Baltimore.
Mark Harrington, head of Treatment Action Group, an Aids activist organisation, said: "We can't afford any more trials like this. We have to stop and reassess and recommit to basic science, or people will begin to lose faith."
However, John Moore, an Aids virologist at America's Weill Cornell Medical College, said: "I do think that what happened in this trial is an example of scientists blindly rushing into dangerous things."
Even before the tests came to a grinding halt, some experts were questioning whether the type of vaccine being looked at would be successful.
Rather than a drug to help ease the effects of the virus, people in areas worst hit by the epidemic were looking for a wholesale cure. As it turned out, the vaccine's abject failure has rendered arguments over marketing unnecessary.
The US National Institutes of Health, which funded both programmes, is holding a crisis meeting next week.
But experts fear a bleak future. "None of the products currently in the pipeline has any reasonable chance of being effective in field trials," said Harvard University molecular geneticist Ronald Desrosiers.
"We simply do not know at the present time how to design a vaccine that will be effective against HIV."
CHICAGO (Reuters) - A dangerous drug-resistant bacterial infection has been showing up in a small number of patients who undergo face-lifts, doctors reported on Monday.
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