This protocol is a multi-center study to evaluate the durability of the immune response following the open label administration of the investigational rVSVdeltaG-ZEBOV-GP vaccine (V920) as pre-exposure prophylaxis for adults who have an occupational risk for potential exposure to Ebola virus. The vaccine uses a live replicating vesicular stomatitis virus (VSV) replacing the gene encoding the G envelope glycoprotein with the gene encoding the envelope glycoprotein from the Zaire strain of Ebola (rVSVdeltaG-ZEBOV-GP also known as V920).