Syag> . It IS deadly, for a large percentage of people. It is NOT ebola.
And this is the source of moral confusions and dilemmas. In face of a deadlier disease, everyone would just stay home for 2 weeks and get rid of it. As it is now, the moment numbers start going down, whether due to SD or vaccines or weather or chance, population increases activity and numbers go up.
We have an analogy in halakha, where more borderline cases require more work (such as karbonos for inadvertent and not purposeful violations).