less lethal than planned

What I don't think they counted on

Assuming the shots and the bug were both intended for large-scale mortality and disease, the other piece they would not have counted on is the resiliency of human biology in the face of new bugs. This would not be surprising. The hubris of these guys with their new toys is classic. They really do believe themselves gods, and they always fail to appreciate how miraculously well-designed the world is (human biology in this case), way way beyond their fondest dreams of being able to do "better". 99% of the time, they will fuck up anything they attempt to improve, and they run into obstacles even in raw attempts at destruction. The complexity of our universe is so far beyond their comprehension that their efforts are pathetic measured against it.