Since smallpox eradication, the science of eradication has changed and with it, our definitions of what diseases are possible to eradicate. However, eradication must not beget complacency. As has been learned from past control or eradication attempts with a variety of viral diseases, from yellow fever to influenza, accidental or intentional reintroduction is a real threat--one that could strike anywhere and for which we need to be fully prepared...