This is because our immune systems are generally blind to the virus and unable to launch
an effective antibody attack. Other challenges that scientists face as
they try to create a vaccine include a lack of good animal models to
study and the virus's ability to constantly change and mutate.
Additionally, although controllers can keep levels of the virus low, no
one has ever fully recovered from HIV infection. This means there's no
natural, winning strategy for scientists to study and try to elicit.