ATLANTA (AP) — The quest for the world's first malaria vaccine appears to have taken a big step.The first results from a late-stage test in seven African countries were released Tuesday. They show the experimental shots cut the number of cases of malaria in half in young children.The vaccine still is at least three years away. More testing must be completed to see how well it works in infants and how long protection lasts. Then the vaccine will be reviewed by government agencies in Europe and in individual African nations.GlaxoSmithKline developed the vaccine. It targets a malaria parasite found in sub-Saharan Africa. There are no plans to market it in the United States.The research results were released at a malaria conference in Seattle.