SARS and MERS each killed fewer than 1,000 people. COVID-19 is already reported to have killed more than twice that number. With its potent mix of characteristics, this virus is unlike most that capture popular attention: It is deadly, but not too deadly. It makes people sick, but not in predictable, uniquely identifiable ways. Last week, 14 Americans tested positive on a cruise ship in Japan despite feeling fine—the new virus may be most dangerous because, it seems, it may sometimes cause no symptoms at all.

https://www.theatlantic.com/health/archive/2020/02/covid-vaccine/607000/