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 the US, Japan, South Korea and Thailand, while there are understood to be at least five suspected cases being tested in the UK.
Now, fears are growing that the increased travel expected over the upcoming Lunar New Year period could aid the spread.
But just how worried should we be in the UK?
– How does this compare with 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 that 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.”
US researchers writing in the journal JAMA also 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.”
– How easily can it be transmitted?
The World Health Organisation (WHO) said on Thursday it was “too early” to declare a public health emergency of international concern.
The body said there is evidence of transmission between people in close contact, such as families or those in health care settings.
But it said it has not seen any evidence of onward transmission.
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.
Health Secretary Matt Hancock said the UK is one of the first countries to develop a test for coronavirus and the NHS is ready to respond to any cases.
He added: “The public can be assured that the whole of the UK is always well prepared for these type of outbreaks and we will remain vigilant and keep our response under constant review in light of emerging scientific evidence.”
The Foreign Office has advised against all but essential travel to Wuhan, but has not changed its advice on other destinations which have reported cases.
– Could cases be confirmed in the UK?
A handful of cases have been identified abroad, including in Japan and the US, but there have been no confirmed cases in the UK.
Officials from Public Health England have been monitoring direct flights from Wuhan city to the UK.
Professor Neil Ferguson, director of the Medical Research Centre for Global Infectious Disease Analysis, said the UK is not a major destination of visitors travelling out of Wuhan.
But, he said: “Border screening and in this case, in the UK, alerting the health system, is not 100% foolproof – there could be a mild case.”
In addition, the screening will only catch people already showing symptoms.
Dr Nathalie MacDermott, NIHR academic clinical lecturer, 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.
“If they were to be unwell at the airport or become unwell in the future it will allow more prompt isolation and testing of the patient, with appropriate tracing of any people the patient may have been in contact with.
“This will hopefully limit the amount of people the person may have contact with while unwell and so limit the spread of the virus.”