I should also add the possibility that it doesn't have to be a government performing these actions. It could simply be one jaded semi-suicidal lab tech that is really mad at the world and realizes they are holding in their hands the power to F the world. Have people thrown their lives away for lesser causes? Or maybe even incompetence? Have lab techs ever mishandled dangerous material?
If you want to use a bioweapon for clandestine economic warfare, you don't actually want to people to die, that draws attention. You just want everyone to be sick at crunch (harvest) time.
The worldwide average estimate (including asymptomatic) is 0.15% - right around the same as the flu (0.05% - 0.1% depending on the year, IIRC).