It is a new coronavirus – that is to say, a component of the coronavirus family that has never been faced before. Similar to other coronaviruses, it has come from animals. Most of those infected either worked or regularly go shopping in the Huanan seafood wholesale market in the centre of the Chinese city, which also sold living and freshly slaughtered animals. New and disturbing viruses usually initiate in animal hosts. Flu and Ebola are examples.

What other coronaviruses have there been?

Middle Eastern respiratory syndrome (Mers) and Severe acute respiratory syndrome (Sars) are both caused by coronaviruses that arose from animals. Though Mers is believed to be spread to humans from dromedaries, the prime hosts for both coronaviruses were perhaps bats. In 2002, Sars spread nearly unchecked to 37 countries, triggering global panic, infecting over 8,000 people and killing more than 750. Mers seems to be less easily transmitted from human to human, but has greater fatality, killing 35% of about 2,500 people who have been affected.

What are the symptoms triggered by the Wuhan coronavirus?

The virus causes pneumonia. Those who have fallen sick are reported to suffer fever, coughs and breathing difficulties. In critical cases there can be organ failure. As this is viral pneumonia, antibiotics are useless. The antiviral drugs we have to fight flu will not act. If people are admitted to hospital, they may get assistance for their lungs and other organs as well as fluids. Recovery will depend on the potency of their immune system. Most of those who have died are known to have been previously in poor health.

Is the virus being spread from one person to another?

China’s national health commission has confirmed human to human spread. By 27 January, the Chinese authorities had accepted more than 2,700 cases and 56 deaths. In the last week, the number of verified infections has more than tripled and cases have been discovered in 13 provinces, as well as the municipalities of Beijing, Chongqing, Tianjin and Shanghai. The infection has also been confirmed outside China, in Macau, Hong Kong, Nepal, Japan, Singapore, South Korea, Thailand, Taiwan, the US, and Vietnam. There have not been any confirmed incidents in the UK at present, with the 14 people tested for the virus all showing negative. The actual number to have caught the virus could be far higher as people with mild symptoms may not have been identified. Modelling by WHO experts at Imperial College London proposes there could be as many as 100,000 cases, with ambiguity putting the margins between 30,000 and 200,000.

How concerned are the experts?

There were worries that the coronavirus might spread more extensively during the week-long lunar new year holidays, which start on 24 January, when billions of Chinese go home to celebrate, but the celebrations have largely been withdrawn and Wuhan and other Chinese cities are in lockdown. At the instant, it seems that people in poor health are at highest risk, like always the case with flu. A key worry is the range of seriousness of symptoms – some people seem to suffer only mild illness while others are becoming severely ill. This makes it harder to ascertain the correct numbers infected and the amount of transmission between people. But the authorities will be eager to stop the spread and will be concerned that the virus could become more powerful than it so far appears.

At what point should you see a doctor if you have a cough, say?

Lest you have recently gone to China or been in contact with someone affected with the virus, then you should treat any cold or cough symptoms as normal. The NHS guides that there is usually no need to visit a doctor for a cough except it is constant or you are having other symptoms such as difficulty breathing, chest pain or you feel very unwell.

Why is this any severer than normal influenza?

We don’t yet know how risky the new coronavirus is – and we won’t know until more statistics comes in. Eighty-one deceases out of 2,827 reported cases would mean a 3% mortality rate. However, this is expected to be an overestimate since there may be a far larger group of people who have been infected by the virus but who have not undergone severe enough symptoms to visit the hospital and so have not been calculated in the data. For assessment, seasonal flu usually has a mortality rate below 1% and is thought to cause around 400,000 deaths each year worldwide. Sars had a death rate of over 10%. Another key unknown, of which scientists should get an evident idea in the coming weeks, is how infectious the coronavirus is. A vital difference is that unlike flu, there is no shot for the new coronavirus, which means it is more difficult for weak members of the population – older people or those with prevailing respiratory or immune problems – to guard themselves. Hand-washing and keeping away from people if you feel ill are important. One logical step is to get the flu vaccine, which will decrease the burden on health services if the epidemic turns into a broader outbreak.

Should we be alarmed?

No. The transmission of the virus outside China is worrying but not an unanticipated development. It increases the probability that the World Health Organization will state the outbreak to be a public health emergency of international worry. The key issues are how infectious this new coronavirus is between people and what percentage become critically ill and end up in the hospital. Often viruses that spread easily incline to have a milder impact.

Healthcare workers could be at threat if they suddenly came across someone with respiratory symptoms who had gone to an affected region. Usually, the coronavirus seems to be hitting older people hardest, with a small number of cases in children.