After back-to-back potentially serious laboratory accidents, federal health officials announced on Friday that they had closed the flu and anthrax laboratories of the Centers for Disease Control and Prevention and have halted shipments of all infectious agents from the agency’s highest-security labs. The accidents, and the C.D.C.'s emphatic response to them, could have important implications for other laboratories around the world engaged in research into dangerous viruses and bacteria. If the C.D.C — which the agency’s director, Dr. Thomas Frieden, called “the reference laboratory to the world” — had multiple accidents that could have, in theory, killed not just laboratory...