Drug holidays mimic what vaccines do.
The success of this strategy is measured by monitoring viral load levels, which is the amount of viral RNA that can be measured in plasma. While the virus has come soaring back in some people, requiring them to restart therapy, it has rebounded to a different degree or plateaued at low levels in others. In fact, what most intrigues scientists is their observation that HIV-specific cellular immune responses are boosted as the virus begins to reemerge. When therapy is stopped and the virus starts to creep back, the immune system gets reactivated, and as the virus rebounds, so do the immune troops. If the theory pans out, each time someone stops and starts therapy the immune response gets stronger and eventually begins to win out over the virus, causing the viral load to plateau.