An experimental vaccine could prove to be the ultimate weapon against AIDS, research suggests.
Studies indicate it has the potential to clear the body of all traces of the AIDS virus, HIV.
Uniquely, the injected vaccine is carried by a persistent virus which remains in the body for life.
Cytomegalovirus (CMV) enables the immune system to be constantly on the alert for HIV.
Researchers in the US used different versions of the vaccine against a monkey form of the AIDS virus, Simian Immunodeficiency Virus (SIV), with outstanding results.
More than half the rhesus macaques monkies 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 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.
The findings suggest the vaccine could be effective enough to rid the body of immunodeficiency virus completely, according to the scientists writing in the journal 'Nature'.
Conventional antiretroviral therapies 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 & Science University's Vaccine and Gene Therapy Institute, said: "The next step in vaccine development 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 as well as tiredness.
People with weakened immune systems can have a more severe response.