Suggestions to make this section more useful are welcome. Progress in developing a vaccine against HIV has been much slower than expected. In spite of years of research into HIV, much is still unknown about the virus. An important part of the research into these questions is done using animal, mostly primate, models. Unfortunately, no single primate model is perfectly suited for the job.
Chimpanzees are the primates genetically most closely related to humans.
They can be infected with HIV, but progress to AIDS very slowly after HIV infection. Even a vaccine that does not prevent infection may still boost the immune system enough to prevent or delay disease in the event of infection. Since chimpanzees develop disease only very slowly, this effect cannot easily be studied using chimpanzee models. In addition, chimpanzees are a threatened species, they are very expensive, they cannot be put down unless they are extremely ill, and since HIV usually does not make them sick they must be kept in isolation for their lifetime, up to 40 years. Being HIV-infected, they pose a risk for their caretakers.