Five researchers at Children's Hospital Oakland Research Institute in California were exposed to live anthrax recently while working to develop a vaccine to protect children from this potentially deadly bacterial infection. The Oakland researchers thought they were working with an inactivated form of bacterium that they received from the Southern Research Institute's Frederick, Md., lab. The mistake became evident after mice injected with the bacterium began to die. None of the researchers has shown any symptoms of infection, but they are being treated with antibiotics as a precaution. The research institute is a mile from the hospital, so patients were never in any danger. Because of their expertise, FBI bioterrorism agents were called to remove the anthrax from the lab. Local and state health officials as well as the Centers for Disease Control & Prevention are investigating why the live anthrax was shipped to the California institute. SRI, which is registered with CDC to handle live anthrax, is also looking into the matter.