As the death toll from the new coronavirus climbs, questions remain about how it spread to humans and how much of a threat it poses across the world.
Cases have been confirmed in China, the US, Japan, South Korea, Thailand, Singapore, Macao, Taiwan and Vietnam, while there are understood to be at least 14 suspected cases being tested in the UK.
Fears are growing that increased travel expected over the Lunar New Year period next weekend could aid the spread.
But just how worried should we be in the UK?
– How does this compare to previous outbreaks?
Several experts say the new coronavirus appears to be less severe than its predecessors.
Paul Hunter, professor in medicine at the University of East Anglia, said typical flu epidemics can kill tens of thousands of people, but previous new coronavirus outbreaks have led to fewer deaths.
For example, severe acute respiratory syndrome (Sars) killed about 800 people, while Middle East respiratory syndrome (Mers) led to about 450 deaths.
Prof Hunter said: "This new strain seems to be rather less lethal than the previous two outbreaks, however this could still change.
"All new outbreaks are worrying, especially in the early weeks when it is not clear how the outbreak could progress.
"I think it unlikely that the Wuhan coronavirus will cause a major public health issue in the UK, in large part because of our existing health system."
The novel #coronavirus (#nCoV) originating in China & now rapidly spreading appears to have a lower fatality rate than SARS- & MERS-CoV; the prospect of a sustained epidemic is uncertain. Classic #publichealth measures (eg isolation) are a primary defense https://t.co/0W4wmbOgLL
— JAMA (@JAMA_current) January 24, 2020
US researchers writing in the journal JAMA said the fatality rate appears to be lower than that of Sars or Mers.
Catharine Paules and colleagues wrote: "The extent, if any, to which such transmission might lead to a sustained epidemic remains an open and critical question."
The World Health Organisation (WHO) said it was too early to declare a public health emergency of international concern, but added: "There is still a lot we don't know.
"We don't know the source of this virus, we don't understand how easily it spreads and we don't fully understand its clinical features or severity."
– How easily can it be transmitted?
Tho WHO said there is evidence of transmission between people in close contact, such as families or those in health care settings.
It said it has not seen any evidence of onward transmission but "that doesn't mean it won't happen".
Dr Andrew Freedman, reader in infectious diseases at Cardiff University, said it is not clear how contagious the virus is.
He said: "This is important in determining the risk of a much larger outbreak developing, with spread to people who have not travelled to Wuhan.
"It is likely that the US and other countries will be considering what further measures are needed to limit the risk of more cases arriving from China."
– What is the risk to the UK?
England's chief medical officer, Professor Chris Whitty, has revised the risk to the UK population from very low to low.
Public Health England (PHE) said it is a "rapidly evolving situation" which officials are monitoring carefully.
If cases are confirmed, people with weakened immune systems, older people and those with long-term conditions are most likely to experience severe symptoms.
Health Secretary Matt Hancock said the UK is one of the first countries to develop a test for coronavirus and it is "always well prepared for these type of outbreaks".
If cases are confirmed, patients will be taken to an airborne high consequences infectious disease centre.
– Could cases be confirmed in the UK?
A handful of cases have been identified outside China, including in Japan and the US, but there have been no confirmed cases in the UK.
📒NEW BLOG: Wuhan novel coronavirus: what you need to know https://t.co/9vOzpEOscA
— Public Health England (@PHE_uk) January 24, 2020
Officials from PHE have been monitoring direct flights from Wuhan to the UK and will expand this to other Chinese departure points if necessary.
Professor Neil Ferguson, director of the Medical Research Centre for Global Infectious Disease Analysis, said the UK is not a major destination for people travelling out of Wuhan.
But he added: "Border screening and, in this case, in the UK, alerting the health system, is not 100% foolproof – there could be a mild case."
Dr Jeremy Rossman, a virologist at the University of Kent's School of Biosciences, said the UK is "likely" to see a confirmed case but the chance of an outbreak is small.
In addition, the screening will only catch people already showing symptoms.
PHE said no checks can offer absolute protection due to the incubation period of the virus.
Dr Nathalie MacDermott, the National Institute for Health Research's academic clinical lecturer at King's College London, said: "It is wise to implement checks at this stage given the evidence on increasing spread of the virus to other countries and across continents, but largely for the purpose of being in contact with travellers from affected regions in case they become unwell."