Dr. Bromage, thank you for this very useful assessment of risk information. I learned as much from this as probably all of the other articles together on CovID 19 that I have read. It is particularly useful to me, because I was contemplating returning to a classroom environment where I would be in a large room with only three or four other people for about three hours, once a week. With 65+ years and high blood pressure, my chances of surviving an infection are not very high. The room has no ventilation (an older church building.) So despite distance and masks, I would become high risk for becoming infected over several class sessions. I can teach via computer. It is more difficult, but creates zero risk of infection.