Scientists have developed a new vaccine that partially protects monkeys from an infection much similar to HIV, a breakthrough which they say could be a new weapon in the battle against AIDS.

Researchers at the University of Utah School of Medicine found that rhesus monkeys which received the new vaccine were 80 to 83% less likely to get infected with the Simian immunodeficiency virus (SIV), a virus which is closely related to HIV, when exposed to it.

The experimental vaccine was engineered to trigger the monkeys' immune systems to fight the virus. Researchers often study the effects of an SIV vaccine in monkeys as a way to understand how to develop an HIV vaccine in humans.

This is an important step toward an HIV vaccine, said Adam Spivak, an HIV researcher at the university.

“This study demonstrates that the immune system can be prepared to respond to, and partially control, viral infection that mimics HIV-1 transmission in humans,“ Spivak said.

At the start of the research, published in the journal Nature, 40 monkeys were injected with either the experimental vaccine or the placebo vaccine, and then given a booster shot at six months. The monkeys were then exposed to SIV six times. Researchers found that those were on the experimental vaccine had a lower amount of virus in their blood than those given the placebo.