> Is that typical of a virus?
A classical theory said that viruses become more contagious but less virulent “in long term” because mutations that kill the hosts do not propagate much. It is understood now that it is not always so, especially given billions of hosts, crampled in large cities and travelling in the airplanes, available for mutations.
on the other hand, even if weapon developer did not think about using virus attacks on such large scale, they for sure are thinking about it now.