Johnson & Johnson stopped a mid-stage test of its HIV vaccine in southern Africa after the shot showed insufficient ability to protect people from contracting the virus. The trial, called Imbokodo, showed the vaccine was just 25 percent effective in preventing HIV infection over a period of two years, short of a goal of 50% efficacy, according to a statement. A similar vaccine developed by the drugmaker will continue being tested in Europe and the Americas in a final-stage study called Mosaico, Paul Stoffels, J&J’s chief scientific officer, said.