A twice-yearly shot could help end AIDS. But will it get to everyone who needs it?

A twice-yearly shot that prevents HIV infections will be available at low cost in 120 poor countries. But nearly all of Latin America was exluded from the deal with drugmaker Gilead, sparking concern the world is missing a critical opportunity to stop AIDS. The shot was 100% effective in preventing HIV infections in a study of women, and results published Wednesday show it worked nearly as well in men. The drug is already sold to treat HIV infections and Gilead plans to seek approval soon to use it to guard against infections.