- last post: 01.01.0001 12:00 AM PDT
It might be that the physiology (spelling) between the Human and various covanant races might not be different enough to be able to use Biological weapons safely against each other. Mutations happen, especially when you design a germ to reproduce as rapidly as possible so as to be able to take out as many bad guys as you want it too.
Another theory might be that the covanant have the advanced technology to counter-act any human made viruses or germs... and I wouldnt find it hard to believe if due to their religous beliefs, the covies dont use them on us.