An experimental HIV vaccine developed by Johnson & Johnson has shown promise after a successful study conducted on monkeys.

The vaccine showed success in protecting six of 12 monkeys infected with a type of HIV specific to primates called Simian Immunodeficiency virus (SIV), according to Reuters.

The report, published Thursday by scientists from Beth Israel Deaconess Medical Center in Boston, suggests that the new vaccine may soon be ready for human trials which are now ongoing and involve 400 volunteers from East Africa, South Africa, the United States and Thailand.

The vaccine works two ways: by delivering HIV proteins to the body, prompting the immune system to create antibodies, and enhancing the response through the booster, composed of "purified HIV proteins."

For the trial, the scientists gave 12 monkeys the "prime-boost vaccine". Another 12 were given only the prime vaccine, while eight were given placebos.

The monkeys then received doses of the HIV, considered to be more infectious compared with the type that humans were exposed to.

Of the 12 that received the prime-boost vaccine, six remained protected from HIV; only two from the prime-only group were protected. On the other hand, monkeys from the placebo group were all infected.

To prove if the vaccine really worked, scientists gave a new group of monkeys blood extracted from the HIV-immunized monkeys and found that the former did not get infected.

The findings that appeared in the journal Science suggest that the two-step vaccine not only provides HIV protection for monkeys, but also helps the immune system produce measurable antibodies that determine how well-protected the animals are.

"We do not know for sure whether a vaccine that protects monkeys will in fact protect humans," said Dan Barouch, lead author of the study, according to News 4 Tucson.

However, Barouch thinks the new vaccine may show promise in humans because it has elicited a strong immune response against an extremely aggressive version of the virus.