From Medical Correspondent Elizabeth Cohen

CHICAGO (CNN) -- The discovery announced this week that humans contracted the HIV virus from chimpanzees may help in the development of a vaccine to protect humans from getting infected, say researchers at the 6th Conference on Retroviruses and Opportunistic Infections.

Unlike humans, when chimps are infected with the primate version of HIV, they do not develop AIDS.

"If we could identify what that factor is -- and there's no guarantee we will, but if we can -- then one could direct your vaccine to elicit a response of that particular factor that is protecting them," said Dr. Anthony Fauci of the National Institutes for Health.

The vaccine effort could use the help. After years of research, only one vaccine is in large-scale clinical trials, and many experts think it will not succeed.

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CNN's Elizabeth Cohen reports on the effort to find an HIV vaccine for humans
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While scientists have been able to come up with effective drugs, such as AZT, to treat people with HIV, they have had a difficult time finding a vaccine to prevent HIV infection.

There are several reasons for the delay in an AIDS vaccine: The first is money -- vaccines are needed most urgently in the poorest countries.

"Massive numbers of vaccines would be needed and companies are concerned, 'who's going to pay for that,'" said Dr. Seth Berkley of the International AIDS Vaccine Initiative.

The slow progress on a vaccine can also be attributed to science.

"(HIV) is a retrovirus, and one that has the capability of inserting itself into a gene -- into the genes of our own cell and hiding there essentially indefinitely, so it shields itself from the surveillance of the body's immune system," Fauci said.

There are also safety problems associated with testing a vaccine for a deadly disease.

A research team in Chicago wants to use a live attenuated vaccine. But when used on monkeys, it kills them.

"But essentially, the answer is only going to be how a vaccine acts in a human being, not how it acts in an animal," said Gordan Nary of the International Association of Physicians in AIDS Care.

Nary says one option is to try the vaccine on terminally ill cancer patients, who have less to lose. He said the Food and Drug Administration has agreed to hear the proposal.