How important is “silent spreading” in the covid-19 epidemic?

FEW STORIESThe EconomistThe Economist Today are as prominent in the study of infectious diseases as that of Mary Mallon, a cook to wealthy families, and also to a maternity hospital, in New York in the early 1900s. As she went from one employer to another, typhoid fever, then deadly in one case in ten, followed in her wake. Public-health officials eventually joined the dots and identified her as a carrier of , the bacterium that causes the disease. What was striking about Typhoid Mary, as the newspapers nicknamed her, was that she herself was healthy—proof that people could harbour and transmit without showing symptoms of the illness it causes.