It really was a no brainer…just observing would answer those questions, the so called miracle cure had side effects, very nasty ones at that, obviously someone jumped the gun on administering the “cure” to all the people it could and i’m sure patients were willing to have a needle stuck in them for such a cure. It never “developed” into a virus because it already was one…just genetically engineered…but we as man are not God…so we are bound to fail somewhere. Pigmentation of the skin is lost, side affects similar to rabies…extremely heightened agression, loss of social skills(as said in the movie) pretty much making a human function like an animal. Look up rabies if you need a better idea. It wasn’t anything the government did, when Will said “God didn’t do this…we did” he meant in our strive to change the world…the way things are…an attempt to be God…we ultimately failed and now it’s royally screwing the human race. The ones who had the cure administered became infected and either A. Died off B. Mutated and spread the infection…it eventually became airborne just like any evolving virus and started infecting humans without direct contact…whereas canines didn’t catch the airborne strain.