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.

A drug currently used to treat certain HIV infections has also, on Wednesday, received approval from the US Food and Drug Administration to be used to prevent HIV. Gilead Sciences, maker of the drug,