Letvin concurs. "We must accept the fact that it may never be possible to attain true sterilizing immunity against HIV with a vaccine

Letvin concurs. "We must accept the fact that it may never be possible to attain true sterilizing immunity against HIV with a vaccine," he says. "What we may have to accept is a vaccine that can decrease the amount of viral replication, leading to a much longer period of clinical latency, a period of non-disease. Even such an imperfect vaccine would be of tremendous benefit in areas of the world where this virus is endemic and treatments are simply not available."

Dr. Bruce Walker

While a viable vaccine has thus far remained elusive, the work taking place in the search has led to numerous scientific breakthroughs. "Research that's been done on HIV has pushed science in multiple different directions," says Dr. Bruce Walker, director of AIDS research at Massachusetts General Hospital. "The molecular virology of HIV, the way in which the virus reproduces itself, the way in which the virus gains entry into cells—all of the discoveries that have been made related to HIV relate to other viruses as well. There are countless examples of investigators who started out working on HIV who have been able to apply the things they've learned in HIV to the study of other viruses."

Fauci agrees. "It's been an extraordinary catalyst in understanding things we never understood before," he says, then adds more soberly, "Right now the advances in HIV research are bringing us closer and closer in some cases to partial solutions, but in other cases to the realization of the formidable task we have ahead."