This sort of vaccine engineering is well understood. The very step of substituting material tends to make the virus non-viable outside of the specialized envir

This sort of vaccine engineering is well understood. The very step of substituting material tends to make the virus non-viable outside of the specialized environments in which it's produced, e.g. they've perhaps knocking out something essential for its normal function in chimpanzees. In a presentation I found from obvious Wikipedia pages they showed how they chose the starting virus out of a large galaxy of candidates, it's safe to bet without further examination it's not very bad for chimpanzees or us, to make development safer and easier. The genes that code for Ebola glycoproteins (proteins with sugars) or critical, outward facing and therefore immune system alerting, parts of them, can't get very far without the rest of the Ebola virus payload. At a very simple level, view it as poking at the immune system with a stick who's end is shaped in the way you want it, have with some precision engineered it. The immune system is going to react if you've done it right, you do expect some fevers and such in some people, but no more. "Fortunately" Ebola is ultra lethal to all primates, so animal models are easy to find, and it could be thoroughly tested on them before trying it on humans.