Dr Harriet Robinson assesses the importance of her research

The new vaccine uses harmless fragments of HIV and protected monkeys from extremely virulent strains of the virus.

The only vaccines that previously showed any promise were "live" vaccines, in which the virus is partly disabled. However, widespread fears that the vaccine could mutate and cause infection has meant this approach is unpopular.

"We challenged the vaccine using a highly virulent virus which normally kills the monkeys in six months, but the vaccine was still effective," research leader Dr Harriet Robinson told BBC News Online.

Four macaque monkeys had no trace of HIV, two had viral loads reduced by 100,000 times

Her team at the Yerkes Regional Primate Research Center, Georgia, US, tried eight different approaches, before singling out one, which protects for at least 62 weeks.

The scientific advance was welcomed by the UK's biggest Aids charity, the Terrence Higgins Trust.

"This is great news," says Andrew Ridley, the charity's director of operations. "This is clearly a step on the way to finding a vaccine for HIV and a vaccine is the only way to end the scourge of HIV."

However, Dr Robinson points out: "We didn't completely prevent infection, but we contained it below the level that we could detect it using very sensitive tests."

Dr Harriet Robinson believes there is a 90% chance a human vaccine will be developed

"That has tremendous implications for extending life expectancy and also for transmission. If you take the viral load way down, you really are going to reduce transmission," she says.

Dr Robinson says that everyone eventually wants to have a foolproof vaccine, but that this new work represents significant progress: "Now, 16,000 people a day around the world get HIV, if we can change that to one person a week, that would be tremendous."

Human trials

Work has begun on the next phase of pre-clinical trials, again using macaque monkeys, and focussing on the doses required. Dr Robinson says her "dream" is to see phase one clinical trials in humans begin within a year.

The final vaccine should be "relatively inexpensive", an important consideration given that the most devastating epidemics of HIV are frequently in poorer countries. At present, the vaccination requires two separate injections of different materials.

Dr Harriet Robinson describes the breakthrough

These are a DNA vaccine and a recombinant viral vector vaccine. The first of these are segments of DNA which code for HIV proteins. The vaccinated person would be primed by these to create the proteins and provoke an immune response.

The second part uses the same DNA but packs it inside a pox virus. The virus is excellent at invading cells and this helps produce very high levels of the HIV proteins inside the cell. The pox virus used was part of the smallpox eradication programme and is known to be safe.

The development of an HIV vaccine has been extremely difficult. HIV eludes the antibodies which should capture viruses invading the body. It also destroys the helper T cells which are vital in co-ordinating the body's immune response.