The U.S. government's smallpox vaccination program, which was intended to begin with immunizations of emergency responders and eventually branch out to volunteers in the general public, may be permanently derailed by the large numbers of medical professionals who have opted not to be vaccinated. So far, 38,000 such workers have been immunized, far below an initial estimate of 450,000 during the project's opening phase. During the second phase, the vaccine will be available to police officers, firefighters, and emergency workers, but the Advisory Committee on Immunization Practices has suggested that the program be held back until reviews of the vaccine's safety profile--including its increased risk for causing myocarditis--are conducted. Julie Gerberding, director of the Centers for Disease Control and Prevention, says that the risk profile for the vaccine has not changed since the program's rollout in December 2002--a view echoed by the state of Florida, which has already begun the second phase of the campaign and has no plans to slow it down.