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Hazardous materials experts enter the Hart Building of the U.S. Senate on Nov. 7, 2001, in Washington. The building was closed after an anthrax-laced letter was found in then-Sen. Tom Daschle's office.

Shortly after 9/11 - there was another scare: letters containing brown anthrax powder showed up in the mailboxes of several media outlets in New York and Florida. They were the first wave in what would later become known as the nation's first bio-terror attack. More than 20 people developed anthrax infections and five died. Since then, the federal government has spent $60 billion on bio-defense efforts. But how safe are we? Here to help us answer that is science journalist Laurie Garrett. She's the Pulitzer Prize-winning author of the book, "I heard the Sirens Scream," a look at the public health impact of 9/11.