SCIENTISTS have made a breakthrough in the battle against Aids after discovering a vaccine with the potential to clear the body of all traces of HIV.
The research, published in the journal Nature, suggests that the new experimental vaccine could prove to be the ultimate weapon against Aids.
And in another promising development, the injected vaccine, which could be given to people after they have been infected with HIV, was carried by a persistent virus which remains in the body for life.
This virus - called cytomegalovirus (CMV) - enables the immune system to be constantly on the alert for HIV and to react if it re-emerges.
Scientists and campaigners yesterday hailed the latest research, which follows previous failed attempts to develop a vaccine to combat HIV.
The researchers in the US used different versions of the vaccine against a monkey form of the Aids virus, SIV (Simian Immunodeficiency Virus), with promising results. More than half the rhesus macaques treated responded to the point where even the most sensitive tests detected no signs of SIV.
To date, most of the animals have maintained control over the virus for more than a year, gradually showing no indication that they had ever been infected.
Unvaccinated monkeys infected with SIV went on to develop the monkey equivalent of Aids, caused by the collapse of their immune systems.
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The findings suggest the vaccine could be effective enough to rid the body of immunodeficiency virus completely.
Conventional antiretroviral therapies now given to patients are able to control HIV infection, but cannot clear the virus from its hiding places within the immune system's white blood cells.
Study leader Dr Louis Picker, from Oregon Health and Science University's Vaccine and Gene Therapy Institute, said: "The next step is to test the vaccine candidate in clinical trials in humans.
"For a human vaccine, the CMV vector would be weakened sufficiently so that it does not cause illness, but will still protect against HIV."
CMV belongs to the herpes family of viruses, and like other members of the group never leaves the body once an infection has occurred.
An estimated half of all adults in the UK carry CMV but suffer no or few symptoms.The virus is spread through bodily fluids such as saliva and urine. When symptoms do occur, they are similar to those of flu including a high temperature and swollen glands and tiredness. People with weakened immune systems can have a more severe response.
Professor Robin Shattock, a professor of infection and immunity at Imperial College London, said: "The breakthrough here is in using a viral delivered vaccine that persists - essentially using an engineered virus to thwart a pathogenic virus. The tricky part will be showing it is safe and effective in humans."Dr Wayne Koff, chief scientific officer at the International Aids Vaccine Initiative, which funded the research, said: "What's exciting about these findings is that for the first time a vaccine candidate has been able to fully control the virus in some animals.
"And surprisingly, the data suggested the possibility that the immune system could eventually eliminate the virus altogether.
"This research gives us potential clues as to how we might design an HIV vaccine for humans that would provide the same type of control. The next step is to adapt this vaccine strategy so it can be tested in human trials."
Jason Warriner, clinical director at HIV charity the Terrence Higgins Trust, said: "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.
"Although this vaccine was found to be partially effective in monkeys, HIV is an incredibly complex virus, with many different strains that we are still learning about.
"While there's still no cure or vaccine, prevention is the only way of protecting yourself so you need to make sure you use condoms when having sex."