Federal health officials announced on Friday that flu and anthrax labs at the Centers for Disease Control and Prevention have been closed, and all shipments of infectious agents have been stopped. The announcement comes after back-to-back lab accidents when staff members may have been exposed to dangerous pathogens that could have spread to the public. In one incident last month, as many as 75 CDC staff members were potentially exposed to live anthrax bacteria when samples were sent to labs unequipped to handle them. In a second incident disclosed on Friday, a CDC lab accidentally contaminated a flu sample with the deadly H5N1 bird flu strain. On top of those incidents, six vials containing a live smallpox virus were recently found stored in a National Institutes of Health laboratory. They had been there since 1954.