The explosive spread of coronavirus was likely caused by 'stealth transmissions' - undiagnosed people with mild symptoms unwittingly spreading the disease, a new study claims.
Infectious-disease expert Jeffrey Shaman believes the actual number of contaminated worldwide is far greater than reports, estimating a million people may have been infected.
The environmental health sciences professor at Columbia University who co-wrote the study published on Monday said social distancing is a must in order to combat seemingly healthy people spreading the virus.
The study in Science journal, which used epidemiological research and mobile phone data, suggests there were half a dozen undocumented infections for every one confirmed case in Wuhan at the start of the epidemic, reports the Washington Post.
Despite only being half as infectious as the documented infections, these stealth cases resulted in at least two-thirds of documented infections, Professor Shaman and his colleagues said.
The spread of Covid-19 peaked in China in just a few weeks but it was only after travel restrictions were imposed and testing dramatically increased on January 23 that undocumented cases became more apparent, the report continues.
Prof Shaman said this flip in the ratios meant about 60 per cent of carriers were confirmed - but fast forward to now and new daily cases have significantly dropped from thousands to tens. READ MORE