The approval could slow new infections and move the world closer to eliminating HIV. But huge obstacles remain.

A new twice-yearly shot could be a "game changer" in the fight against AIDS, but experts' hopes have dimmed because of the current political climate.

The U.S. has approved the world’s only twice-a-year shot to prevent HIV, the first step in an anticipated global rollout that could protect millions – although it's unclear how many in the U.S. and abroad will get access to the powerful new option.