If I understand correctly, the hard part safetywise is not making the vaccine, handling it and giving it to the monkeys. It's the fact that you then have to giv

If I understand correctly, the hard part safetywise is not making the vaccine, handling it and giving it to the monkeys. It's the fact that you then have to give the monkeys real Ebola to see if the vaccine worked. So the hard part is handling real Ebola and monkeys infected with it. What these guys have done is broken that real Ebola into two pieces, where one piece is only in the monkeys. So even in the worst case scenario that a monkey infects a human with "real" Ebola when they are testing the vaccine efficiency, the "real" Ebola is now unable to replicate itself in the human body. It's very clever. Edit: so I think the answer by k_sze is wrong, but I'm not sure. Is there an immunologist in the room?