The Centers for Disease Control and Prevention is enrolling volunteers in a Sierra Leone clinical trial that will assess the safety and efficacy of a candidate Ebola vaccine in about 6,000 health and other frontline workers. All study participants will receive the rVSV-ZEBOV vaccine and be followed closely for six months. Results from early studies show an acceptable safety profile and indicate the candidate vaccine produces an immune response, the agency said. “A safe and effective vaccine would be a very important tool to stop Ebola in the future, and the frontline workers who are volunteering to participate are making a decision that could benefit health care professionals and communities wherever Ebola is a risk,” said CDC Director Tom Frieden, M.D.