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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.

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(Image: REUTERS)

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.

(Image: JEROME FAVRE/EPA-EFE/REX)

Is it safe to take ibuprofen for coronavirus symptoms? The NHS has stopped advising coronavirus patients to take ibuprofen amid concerns the anti-inflammatory painkiller could only make things worse. A statement read: "There is currently no strong evidence that ibuprofen can make coronavirus (COVID-19) worse. "But until we have more information, take paracetamol to treat the symptoms of coronavirus, unless your doctor has told you paracetamol is not suitable for you. "If you are already taking ibuprofen or another non-steroidal anti-inflammatory (NSAID) on the advice of a doctor, do not stop taking it without checking first."

The study says a "radical increase in the identification and isolation of currently undocumented infections would be needed to fully control” the novel coronavirus.

People in the UK, meanwhile, have been told to avoid pubs, clubs and restaurants and work from home wherever possible to slow the spread of coronavirus which has now claimed 55 lives in the UK.

Prime Minister Boris Johnson said at a press conference yesterday urged everyone to "stop non-essential contact and to stop all non-essential travel”.

The PM said London appeared to be “a few weeks ahead” of other areas and urged people in the capital to pay special attention to the measures – including home working – suggested by the Government.

The UK death toll yesterday rose to 35 while there have now been 1,543 cases.

Health Secretary Matt Hancock yesterday said that over-70s could be asked to self-isolate for four months.

Across the world more than 6,000 people have now died from the disease.