jeremy howard is a distinguished research scientist at the university of san francisco. he wrote those words for "the washington post." mr. howard, the w.h.o. initially said you only need to wear a mask if you're taking care of a person with a suspected covid-19 infection. how did they get tell so strong? >> well, we now know that 50% of people infected have no symptoms. we also know during the first week is when people are most infectious, where they're least likely to have symptoms. what the w.h.o. did here, they did not err on the side of caution. they weren't quite sure of the science, and what they should have said is do do it. 80% of americans wear a face mask, any kind of cover, they can actually stop the virus in its tracks. >> here is the cloth covering i'm using, i don't know if you can see it, when i wear it, am i doing so to protect myself or to protect you? >> primary, you're doing it to do your bit in the community to protect others. we know that this disease spreads when we talk, little droplets fly out of our mouth. it makes obvious sense and the science