That's precisely why he doesn't think the virus can be stopped. Viruses like SARS, MERS, and the avian flu were eventually contained in part because they were more intense and had a higher fatality rate. In other words, if you were infected by the virus that caused SARS, chances were you weren't out and about. But because the current coronavirus, known as COVID-19, can be asymptomatic, or at least very mild, there's a better chance people will likely go about their day as normal. The down side, though, is that it becomes harder to trace and prevent. In that sense it's similar to the flu, which can also be deadly, but often passes without the infected person seeking medical care.