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. While a vaccine to prevent HIV still is needed, some experts say the shot made by Gilead Sciences — a drug called lenacapavir — could be the next best thing. It nearly eliminated new infections in two groundbreaking studies of people at high risk, better than daily preventive pills they can forget to take.