PROJECT SUMMARY/ABSTRACT Crimean-Congo hemorrhagic fever virus (CCHFV) is a tick-borne emerging pathogen that causes severe and often fatal hemorrhagic fever in humans across a broad geographic range that includes more than 30 countries. The NIAID lists CCHFV as a Category A priority pathogen, a biological agent that poses the highest risk to national security and public health. CCHF is of particular importance to public health as there are no licensed vaccines or treatments available for use in humans, and because of the concern that the virus could be used as an agent of biological terrorism. The goal of this project is to advance the development of a recombinant vaccine based on next generation vesicular stomatitis virus (rVSV) vectors expressing the CCHFV glycoprotein as a potential medical countermeasure that can provide protection across all six genetically distinct clades of CCHFV. This application proposes to develop and pre-clinically validate a rVSV vectored CCHF vaccine. Next generation Vesiculovax™ CCHF vaccines will be compared head-to-head with a prototype rVSV vaccine that has been shown to completely protect animals against lethal CCHFV infection. Vaccines will be compared for immunogenicity, lack of neurovirulence, and the ability to protect STAT-1 knockout mice against all six M segment clades of CCHFV. A lead candidate vaccine will then be down selected. Supporting studies using a newly developed lethal nonhuman primate model of CCHFV will be employed to confirm protective efficacy of the lead vaccine candidate, assess the ability to the vaccine to provide rapid protection, and finally to begin to determine correlates of protection. This proposal will draw together expertise in vaccine development, CCHFV biology, and animal modeling needed to develop a vaccine that meets both the outbreak and bioweapon scenarios that require rapid protection against all CCHFV clades with a single administration.