In most cases you put the masks on the sick. The closest disease we have for comparison is the original SARS and we stopped it because symptoms showed (and cou

In most cases you put the masks on the sick. The closest disease we have for comparison is the original SARS and we stopped it because symptoms showed (and could be tested in bulk by thermal cameras) before people were infectious. Covid has turned into a pandemic because it has the unexpected property of most infection being before symptoms show.