Silent spread of virus keeps scientists grasping for clues

One of the great mysteries of the coronavirus is how quickly it rocketed around the world. As workers return to offices, children prepare to return to schools and those desperate for normalcy again visit malls and restaurants, the emerging science points to a menacing reality: If people who appear healthy can transmit the illness, it may be impossible to contain. Researchers have exposed the frightening likelihood of silent spread of the virus by asymptomatic and presymptomatic carriers. But how