If they made it too deadly and with significant medical effects that happen too fast, it would be too obvious. As it is, they are able to significantly reduce the population over a several year period without it being noticeable to the general public.
If they made it too deadly and with significant medical effects that happen too fast, it would be too obvious. As it is, they are able to significantly reduce the population over a several year period without it being noticeable to the general public.