The real number of coronavirus cases is more than 75,000, according to a scientific model that says the outbreak will double in size every 6.4 days

• A new study suggests that official figures for the scale of the Wuhan coronavirus outbreak have been far too low.
• The study, published in the prestigious Lancet journal, projected that as of January 25, there were 75,815 people infected in Wuhan. At the time the official figure was 761.
• The study also projected that the epidemic will double in size every 6.4 days.
• It dismissed a lockdown in Wuhan as "negligible," since the virus had already spread by the time it was implemented.
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The true number of people infected with the deadly Wuhan coronavirus is more than 75,000, according to a scientific model, which claims the official number for those infected is far too low.

Academics at the University of Hong Kong published a paper on Friday in The Lancet, a prestigious medical journal, estimating the rate at which the virus is spreading.

It used official data on the number of infections to calculate what it said was the true extent of the disease - almost 100 times the official figures.

Underpinning the analysis is the idea that the number of international cases is disproportionately high given the number of people who travel from Wuhan to other countries.

The academics used the international figures to reverse-engineer a total for the number of cases among greater Wuhan's population of around 19 million.

They said that, as of January 25, they estimated that the number of cases was 75,815.

According to CNN, the official total on January 25 for the whole of Hubei province, which includes greater Wuhan, was 761, barely 1% of the total projected by the scientists.

The paper is not the first to suggest that the official figures do not adequately capture the scope of the outbreak. A paper from Imperial College London published on January 17 suggested that the figures were too low by a factor of 35.

As part of their model, the Hong Kong academics predicted that the scale of the virus would double every 6.4 days. By that logic, the number of people in greater Wuhan with the virus as of this Friday (January 31) would be 151,630.

The official number of cases on January 31 was less than 10,000. The number increased to around 12,000 as of February 1 local time.

The authors of the study said they had taken into account the effect of the dramatic lockdown imposed on Wuhan and surrounding cities last week.

However, they said that its overall effectiveness would be "negligible" given that a critical mass of cases had already been observed in several other cities.

In a meeting on Thursday, the World Health Organization declared the coronavirus outbreak a global health emergency.

On Friday, the US government announced a ban on any foreigner entering the country within 14 days of being in mainland China. It said US citizens would be allowed to enter but placed in quarantine.