The coronavirus’ “case-fatality rate” could range from 1% up to 18%, research suggests.
Since the previously unknown strain emerged in the Chinese city Wuhan at the end of last year, it has crossed national borders into at least 27 countries.
More than 40,500 cases have arisen globally, of which 40,195 are in mainland China, according to John Hopkins University.
The UK has eight confirmed cases.
The death toll reached 908 on Monday, up from 636 the previous Friday.
With more people succumbing to the infection, scientists from Imperial College London set out to uncover what percentage of the infected are dying.
What is the new coronavirus’ estimated case-fatality rate?
Case-fatality rates measure the number of deaths from a certain disease as a percentage of the total amount of patients.
Based on available data, the Imperial scientists estimate the case-fatality rate in the province Hubei - of which Wuhan is capital - as 18%.
They note the “credible interval” ranges from 11% up to 81%.
Among “travellers outside mainland China”, the case-fatality rate is estimated at between 1.2% and 5.6%, with “substantial uncertainty”.
Taking into account both asymptomatic and symptomatic incidences, the scientists calculated the likely overall case-fatality rate to be around 1%.
This was based on the testing of passengers on “repatriation flights” between Japan and Germany early on in the epidemic or from cases reported outside mainland China.
They note differences between countries comes down to “the sensitivity of surveillance systems”.
The scientists stress “all estimates should be viewed cautiously” given the “deaths and cases in mainland China is unclear”.
Scientists from the University of Hong Kong previously gauged more than 75,000 people could have battled coronavirus in Wuhan alone.
Experts have warned patient data is based on hospital cases, which are by definition severe.
There may well be milder cases in the community that never get spotted.
“During an evolving outbreak, there will be many more people with mild symptoms, not requiring any medical intervention,” said Dr Bharat Pankhania from the University of Exeter.
“These people will also be unlikely to go to their doctors.
“Thus, mild illness or illness with minimal symptoms, lack of doctors and lack of resources to go to the doctor could all add up to the true extent of the number of people infected being significantly higher than current estimates.”
He added: “There is a concern around countries with underdeveloped healthcare systems.
“With larger numbers of people infected, there will be considerable circulation of the virus and potential to infect many more people.
“These countries have poor healthcare facilities, and minimal facilities for testing and centrally recoding data, which could mean a gross underestimate of the number of people infected.”
The new coronavirus has been confirmed in Malaysia, Taiwan, Vietnam and Cambodia.
The Imperial scientists also stress it can take up to three weeks for a patient to develop symptoms, be diagnosed and “the final clinical outcome” to be observed.
All this can skew estimates of the case-fatality rate.
“This is reminiscent of the 2009-nH1N1 influenza strain [bird flu], where initial estimates were also much higher than the now more established less than 0.1% [fatality] rate overall,” said Professor Martin Hibberd from the London School of Hygiene & Tropical Medicine.
“It is worth noting though, despite this apparently low fatality rate for 2009-nH1N1, this pandemic caused serious additional problems (compared with typical seasonal influenzas) to healthcare systems worldwide, showing why governments have placed such importance on this new coronavirus virus even as the case fatality rate drops.”
What is the new coronavirus?
Coronaviruses are a class of pathogens, which cause everything from the common cold to the severe acute respiratory syndrome (Sars) outbreak that killed 774 people in 2004.
Six strains are known to infect humans, with the new virus - 2019-nCoV - being the seventh.
Authorities were famously tight-lipped about Sars, not informing the World Health Organization until 11 February, when 305 cases - and five deaths - had occurred across six districts in the province Guangdong.
By 21 March, suspected and probable cases reached 350 - including 10 deaths - in 13 countries.
On 31 March, 1,622 people were infected, of which 58 died.
Genetic analyses reveal 2019-nCoV is more similar to Sars than any other coronavirus.
Scientists from Fudan University in Shanghai found the new strain appears to be 89.1% genetically similar to “a group of Sars-like coronaviruses”.
With Sars having started in bats, this suggests the nocturnal creatures may also be responsible for the new coronavirus.
The virus is thought to have “jumped” from an animal to a human at a live seafood and animal market towards the end of last year.
Most of those who initially became unwell worked at, or visited, the market.
Sars jumped from bats to humans via the masked palm civet, a mammal native to the Indian subcontinent and south-east Asia.
Scientists from Peking University in Beijing have suggested snakes may have been the “intermediate host” for the new coronavirus.
A team from South China Agricultural University have since found pangolins could be to blame.
While little is known about exactly where the virus came from or how long it takes to cause symptoms, Chinese authorities have confirmed it spreads via droplets expelled while sneezing or coughing.
It is unknown whether the virus “floats” in the air or survives on hard surfaces.
Infected patients develop flu-like symptoms, such as fever and breathlessness.
In the most severe cases, victims succumb to pneumonia.
This comes about when a respiratory infection causes the alveoli (air sacs) in the lungs to become inflamed and filled with fluid or pus.
The lungs then struggle to draw in air, resulting in reduced oxygen in the bloodstream.
“Without treatment the end is inevitable,” said the charity Médecins Sans Frontières.
“Deaths occurs because of asphyxiation.”
The US Centers for Disease Control and Prevention has warned there is no specific treatment for coronaviruses.
If the infection triggers pneumonia, doctors work to combat the complication.
Pneumonia is generally caused by bacteria, which tend to respond to antibiotics.
When a virus is to blame – like 2019-nCoV – it may be treated via “antiviral medication”.
Professor Peter Horby from the University of Oxford claims, however, there is “no effective anti-viral”, with treatment being “supportive”.