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A Key To An AIDS Vaccine?

You'd hardly expect Dorothy Muinde to be on the leading edge of the fight against AIDS. For more than 15 years, she has worked as a prostitute in the Nairobi slum called Majengo.

Muinde says she sees about five clients a day. They each pay her about 50 shillings, which is about 80 cents in U.S. currency.

Unprotected sex left Muinde with six children and took the lives of all but a few of her friends, reports CBS News Correspondent John Roberts.

"AIDS in Majengo is very big," she says. "Especially in the younger generation. Every month they are burying five or six women and boys."

So it is with a sense of duty that Muinde makes her twice monthly visit to the health clinic in Majengo for a checkup and to give blood samples to help doctors understand why -- despite repeated exposure to HIV -- she doesn't get infected.

"Sexual exposure to maybe minimal amounts of HIV, sexually, that is what sets the ball rolling," says Dr. Omu Anzala.

Anzala is studying Muinde and 60 other Majengo prostitutes who are, by all appearances, immune to HIV. He believes mild exposure to the virus primed their immune system to recognize HIV and kill it before it takes hold.

"If you can mimic that, then you can develop a vaccine, a vaccine that is preventative," Anzala says.

In fact, Anzala and his colleagues at the University of Nairobi have done just that -- created a vaccine based on that immunity that will begin testing later this year.

Nowhere is a vaccine more urgently needed than in Africa, where in some countries, 25 percent of young people are infected with HIV. And unlike the United States, where modern drugs have drastically reduced the number of people who develop AIDS, here, virtually every case is a death sentence.

In the Majengo clinic, Dr. Joshua Kimani has lost a third of his 2,000 patients.

"The only thing I can do is talk to them, treat the opportunistic infections and watch them die," Kimani says.

That overwhelming frustration is slowly giving way to hope. Doctors in Kenya say their vaccine may work where others have failed, because it fires up the immune system to fight HIV in a whole new way.

"If this approach pans out and this vaccine works, it will mean that science has been looking in the wrong direction for 10 years," says Dr. Francis Plummer.

Muinde has been helping to make a difference, insisting her clients use condoms and spreading the word about safe sex around Majengo. But in a part of the world where many people still believe that AIDS comes from witchcraft, a vaccine is the only way to stop the epidemic.

Reported By John Roberts