My completely unscientifical opinion is that you can’t sterilize the breath/droplets exhaled by CV carriers. Nor will a mask protect others unless that mask is sealed to the face of the infected person. What I’m reading is that the longer people are in a space together, the more hazardous it is. So dashing in and out of the grocery store is not so risky. Sitting next to (or even six feet away from) people in church, at a concert, and certainly for hours on an airplane is quite risky. YMMV.