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Scientists say they have created an anti-HIV drug so powerful that it could work as a vaccine.

Macaque monkeys given the drug were able to fend off high, repeated doses of the simian version of the disease.

The protein-based drug has been 'astonishingly effective' at blocking every major strain of HIV tested, marking a major step towards a cure for AIDS, the researchers claim.

Scientists say they have created an anti-HIV drug so powerful that it could work as a vaccine. Macaque monkeys given the drug were able to fend off high, repeated doses of the simian version of the disease. Pictured is an image of HIV particles infecting a human cell

The technique works by using gene therapy to introduce a new section of DNA inside healthy cells.

'We show a way to achieve long-lived, effective vaccine-like protection from HIV 1', said study leader Michael Farzan, a professor at the Scripps Research Institute in Florida.

The prototype drug, called eCD4-Ig, is made up of two imitations of the receptors, or docking points, where HIV latches on to CD4 cells — the key defences of the immune cells.

The mimics latch on to the virus, tricking it into prematurely launching the docking procedure.

The virus can only execute the procedure once, rendering it unable to attach to CD4 cells.

The scientists likened the effect to closing the door to an intruder and tossing away the key.

The drug provides 'very, very strong protection,' Professor Farzan said who wants to conduct human trials 'soon'.

The team undertook a 40-week experiment which showed that inoculated animals thrived even after being injected with four times the dose needed to infect macaques in a 'control' group.

Further research, to be unveiled at a conference in Seattle next week, found that the treated macaques 'continue to be protected from eight times and 16 times the infectious dose, more than a year after inoculation,' Professor Farzan said.

The search for a vaccine has been one of the most frustrating chapters of the AIDS saga.

Traditional antibody-based candidate vaccines have failed to put up more than a partial shield, partly because of mutations in the stealthy virus.

'This is an exciting new approach, but until the vaccine has been trialled in humans, there's no way of knowing how effective it will be,' said Dr Shaun Griffin, director of External Affairs at Terrence Higgins Trust

The new prototype formula, though, targets sites on the virus' so-called Env entry protein that are 'highly conserved' -  a scientific term meaning that these sites do not mutate very much.

Lab-dish tests have found that the drug also works on human HIV, which is very close to simian version of the virus.

'Of course, we still need to do further safety studies in both macaques and humans,' before any trials can take place, Professor Farzan stressed.

'This is an exciting new approach, but until the vaccine has been trialled in humans, there's no way of knowing how effective it will be,' said Dr Shaun Griffin, director of External Affairs at Terrence Higgins Trust.

The team undertook a 40-week experiment which showed that inoculated monkeys thrived even after being injected with four times the dose needed to infect macaques in a 'control' group

'Although this vaccine was found to be effective in monkeys, HIV is an incredibly complex virus, with many different facets that we are still learning about.'

Since 1981, about 78 million people have been infected by the HIV virus which destroys immune cells and leaves the body exposed to tuberculosis, pneumonia and other opportunistic diseases.

Thirty-nine million have died, according to UN estimates.

Antiretroviral drugs, invented in the mid-1990s, can treat infection, but cannot cure it or prevent it.

Treatment is lifelong and carries side-effects. For many health systems, the drugs bill is spiralling, becoming a major burden to budgets.