The first Aids vaccine to be tested on humans does not protect the general population, but may protect black and Asian people, a US biotech company has announced. The company, VaxGen, has completed a three-year study involving more than 5,000 volunteers. Initial results show the vaccine only reduced the rate of HIV infection by 3.8%, VaxGen said in a statement. Black and Asian people who were given the vaccine, however, had a 67% lower rate of infection than those who received a placebo shot. But these subgroups were small, which means the results have to be treated with caution.