This twice yearly shot could help end AIDS

The shot was 100% effective in preventing HIV infections in a study of women

It's been called the closest the world has ever come to a vaccine against the AIDS virus.The twice-yearly 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.

Drugmaker Gilead said it will allow cheap, generic versions to be sold in 120 poor countries with high HIV rates—mostly in Africa, Southeast Asia, and the Caribbean.

But it has excluded nearly all of America, where rates are far lower but increasing, sparking concern the world is missing a critical opportunity to stop the disease.