DR Congo has begun a vaccine trial in the middle of what health officials have described as a historic Ebola outbreak. The complication is the strain driving this emergency: Bundibugyo has never had an approved vaccine to stop it. Authorities have therefore pushed a different candidate vaccine into testing, a step that puts an unproven product to work in a live epidemic setting. Bundibugyo has appeared in earlier outbreaks in Central and East Africa, yet it has attracted far less vaccine research than the Zaire strain. Existing licensed shots were built for Zaire, which is why the established toolbox now falls short of what the situation demands. Scientists running the trial will watch how recipients respond and whether transmission slows in affected communities. A working vaccine against this strain would give the region a tool it has never possessed, though firm results will take time to produce.