Chimpanzees are our closest genetic relatives, which in some ways makes them excellent stand-ins as research subjects for serious diseases. And, in the case of HCV, they are the only other species that can contract the virus. But there are some concerns, both scientific and ethical, about using them as subjects for HCV research. One issue is that their physiology is just different enough from ours that they actually handle the virus more effectively. In humans, about 20 percent of people are able clear the virus from their bodies spontaneously, meaning that they need no treatment. In chimpanzees, the clearance rate is about three times higher. Because of these physiological differences, Dr. Jeffrey Kahn, who headed the IOM committee, said that "HCV presents somewhat differently in chimpanzees than in humans."

That fundamental problem aside, the committee members remained split on whether chimpanzees should be used in a specific area of HCV research: the development of a prophylactic, or preventive, vaccine. This is one of the two major approaches in HCV research -- the other being how to treat people already infected. The committee agreed on the second issue: Since there are so many humans already infected with HCV, infecting chimps would be unnecessary. "Safety concerns could be addressed by testing new drug candidates in other animal models," Kahn said.

The development of a prophylactic HCV vaccine poses more problems, largely because studies to test the efficacy of such vaccines require what are known as challenge studies, in which animals must be intentionally inoculated with the virus. "Challenge studies for a preventive HCV vaccine aren't ethical in humans," Kahn said. "If such challenge studies are deemed necessary -- and the committee was evenly split on their necessity -- the only alternative animal model at the moment is the chimpanzee."

Since the committee was unable to come to a consensus on this issue -- which is clearly not a minor one -- what will happen? The question is especially relevant since the NIH swiftly agreed to abide by the IOM's recommendations, recently releasing a statement to this effect.

Despite remaining disagreement within the IOM committee over whether the chimpanzee is necessary for HCV preventive vaccine research, the NIH will use the IOM's recommendations to evaluate new research projects. They'll require that proposed studies involving chimpanzees fulfill the following criteria as recommended by the IOM committee: