the thing about Blight-class strategic biowar dolls is that they don't know they're dolls.
they know how to make friends, they love to cuddle, they're so easy to talk into bed, they have the cutest most adorable sneezes.
it's so confusing when everyone around them gets sick.
oh well. what's a Blight-class to do but sigh? she might briefly wonder why she was spared, pack up her life, and move on to a town where everyone's healthier.
rarely, the carriers of the most virulent plagues realize what they are. being the last one left "alive" will do that. paralyzed by horror, they're easy pick-ups for our brave boys and girls in hazmat suits… if they don't self-terminate, anyway.
those built to spread lesser illness, to degrade and debilitate rather than destroy, can circulate almost indefinitely. they're pretty and pleasant enough that public health and border control tend to simply wave them past.
fortunately for us, conditioning keeps them from getting too far from the targets they think of as "home".