new york one of the great mysteries of the coronavirus is how quickly it rocketed around the worldit first flared in central china and within three months was on every continent but antarctica shutting down daily life for millions behind the rapid spread was something that initially caught scientists off guard baffled health authorities and undermined early containment efforts the virus could be spread by seemingly healthy peopleas 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 containit can be a killer and then 40 percent of people dont even know they have it said dr eric topol head of scripps research translational institute we have to get out of the denial mode because its realresearchers have exposed the frightening likelihood of silent spread of the virus by asymptomatic and presymptomatic carriers but how major a role seemingly healthy people play in swelling the ranks of those infected remains unanswered and at the top of the scientific agendathe small but mighty coronavirus can unlock a human cell set up shop and mass produce tens of thousands of copies of itself in a single day virus levels skyrocket before the first cough if one ever arrives and astonishing to scientists an estimated 4 in 10 infected people dont ever have symptomsfor control to actually keep the virus from coming back were going to have to deal with this issue said rein houben a disease tracker at the london school of hygiene and tropical medicinethe dire toll of more than 580000 worldwide deaths from the coronavirus has faded to the background as cities lift restrictions but the slyness of the virus remains on the minds of many scientists who are watching societies reopen wondering what happens if silent spreaders arent detected until its too latetravelers with no coughs can slip past airport screens workers without fevers wont be caught by temperature checks people who dont feel tired and achy will attend business meetingsand outbreaks could begin anewthe first hintsas early as january there were signs people could harbor the virus without showing symptoms a 10yearold boy in china who traveled to wuhan had no symptoms but tested positive along with six others in his family who had coughs and fevers more troubling was a report out of germany a business traveler from china spread the virus to colleagues in munich even though she appeared healthystill many scientists remained unconvinced some questioned whether the chinese businesswoman truly didnt have symptoms they suggested she might have had mild ones she attributed to jet lagthe concept of people unwittingly spreading disease has never been an easy one to grasp from the polio epidemic of midcentury america to the spread of hiv decades laterat the turn of the 20th century a seemingly healthy new york cook named mary mallon left a deadly