Australian researchers say they are a step closer to a vaccine for HIV and hope to be able to offer a preventative jab within the decade.

Experts at The University of Melbourne have found that people with HIV produce antibodies which trigger the immune system to find and attack the virus.

The antibodies force the HIV virus to change, making it weaker.

Professor Stephen Kent says if a vaccine could produce the antibodies so they would work before infection, then that would be likely to prevent infection altogether.

"Because the antibodies don't develop until after they catch HIV, the antibodies can't actually cure the HIV once it's already there," he said.

"The thing about antibodies is, if you can induce them before you acquire infection, it's likely to prevent infection altogether.

"If a vaccine was to make these antibodies it could prevent the virus altogether."

Work on such a vaccine is underway.

About 30 million people around the world are affected by HIV, including 20,000 Australians, and the number is on the rise.

- AAP