HIV is evolving to become less deadly and less infectious, according to the findings of a study published in the journal "Proceedings of the National Academy of Sciences" on December 1.
According to researchers at the University of Oxford, the virus is being "watered down" as it adapts to the immune systems.
The team says it is taking longer for HIV infection to cause AIDS and that the changes in the virus may help efforts to contain the pandemic.
"HIV adaptation to the most effective immune responses we can make against it comes at a significant cost to its ability to replicate," Philip Goulder, who led the study, said.
"Anything we can do to increase the pressure on HIV in this way may allow scientists to reduce the destructive power of HIV over time."
The World Health Organization (WHO) says there are more than 35 million people around the world currently infected with HIV, and AIDS has killed around 40 million people since it began spreading 30 years ago.
HIV rapidly mutates to evade and adapt to the immune system, which reduces its ability to replicate.
That in turn makes the virus less infectious, meaning it takes longer to cause AIDS.
This weakened virus is then spread to other people, beginning a cycle of "watering-down" HIV.
Goulder’s team conducted the study in Botswana South Africa, where they enrolled more than 2,000 women with HIV.
The findings also suggest antiretroviral drugs used to treat HIV/AIDS are forcing the virus to evolve into milder forms.
The researchers developed a mathematical model, which concluded that "selective treatment" of people with low immune cell counts will "accelerate the evolution of HIV variants with a weaker ability to replicate."
That means the drugs would primarily target the nastiest versions of HIV while encouraging the milder ones to thrive.
But the researchers cautioned that a watered-down version of HIV remains dangerous and can still cause AIDS.
"Overall, we are bringing down the ability of HIV to cause AIDS so quickly," Goulder said. "But it would be overstating it to say HIV has lost its potency -- it's still a virus you wouldn't want to have."
Also on December 1, the ONE Campaign group fighting HIV said the world had reached "the beginning of the end" of the AIDS pandemic.
In a report marking World AIDS Day, ONE said that for the first time in the epidemic's history, the annual number of new HIV infections is lower than the number of HIV positive people being added to those receiving treatment.
"We've passed the tipping point in the AIDS fight at the global level, but not all countries are there yet, and the gains made can easily stall or unravel," cautioned Erin Hohlfelder, ONE's director of global health policy.
The United Nations AIDS agency says that some 13.6 million people had access to AIDS drugs by June 2014, a dramatic improvement on the 5 million who were getting treatment in 2010.
ONE also said HIV is increasingly concentrated among hard-to-reach populations such as injecting drug users, gay men, and sex workers.
These groups are often stigmatized and have trouble accessing treatment and prevention services.
With reporting by AFP, Reuters, and BBC