Johnson & Johnson has started clinical trials of its experimental Ebola vaccine, which uses a booster from Denmark's Bavarian Nordic, making it the third such shot to enter human testing. The initiation of the Phase I study, which had been expected about now, marks further progress in the race to develop a vaccine against a disease has killed more than 8,000 people in West Africa since last year. Two other experimental vaccines, one from GlaxoSmithKline and a rival from NewLink and Merck, are already in clinical development. U.S.-based J&J said on Tuesday it had produced enough vaccine to treat more than 400,000 people, which could be used in large-scale clinical trials by April 2015, and a total of 2 million doses would be available through the course of 2015.