To know whether social distancing efforts are helping slow the spread of the coronavirus, and to gauge how long we should go on this way, scientists need to know how many people have mild or asymptomatic cases of COVID-19. There could be many such people. Since their symptoms are vague and possibly nonexistent, the case numbers that climb by the day aren’t what they seem. The true numbers may be much higher — or only a little higher.
Understanding the mild cases can help researches get a handle on the spread of the disease — how it’s spreading and how widespread it’s already become.
Jeffrey Shaman, a professor at Columbia University who studies how the environment affects infectious diseases, has gathered evidence that in China, the epidemic was driven by a lot of not-very-sick people. He estimates that about 86 percent of infections early in that outbreak were transmitted by people who never got sick enough to go to the doctor.