A genetically engineered AIDS vaccine made with the virus used in smallpox vaccinations soon will be tested on volunteers at six university medical centers, the National Institute of Allergy and Infectious Diseases says. Each of the medical centers will recruit nine volunteers to first determine the vaccine's safety and its ability to produce an immune response. There is no chance of contracting AIDS from the vaccine since it contains no live or killed human immunodeficiency virus that causes the deadly disease, the institute said Wednesday. While the institute is conducting numerous research projects to find effective drugs to treat HIV victims, this is only the second vaccine to be approved for testing. The first study began a year ago.