Women and girls have been at the center of the HIV prevention research agenda for more than a decade. Women account for half of new HIV infections worldwide, in part because there are too few prevention options that they can control.

This week, we witnessed a watershed in the global AIDS response: the U.S. Food and Drug Administration approved the first-ever drug to reduce the risk of sexually acquired HIV infection in adults.

If the world acts with strategy and speed to implement the proven and emerging options, the epidemic should be on a measurable downward trajectory over the next five to ten years. Why, then, do we still need an AIDS vaccine? Because we want to end the epidemic.

Last Thursday, on World AIDS Day, President Obama threw the full weight of the U.S. government behind a vision that would have seemed outlandish until now: The end of the global AIDS epidemic.