There have now been more than 31,000 cases of coronavirus, which has been declared a global health emergency. The disease has spread to many countries, including the UK. The answers to a selection of readers' questions about the new virus are below. How safe is it to travel in and out of countries that haven't stopped flights? - Jason Riches, Colchester It is worth remembering this is almost exclusively an outbreak in China. At the moment, more than 99% of cases are in China and the majority of those are in just one province (Hubei). The Foreign and Commonwealth Office advises against all travel to Hubei and against all but essential travel to the rest of mainland China. But no travel restrictions are currently advised for other countries. How come a Chinese doctor in his mid-30's has died from this 'flu-like' virus? I thought it is just babies and the elderly who are at risk? Jeffrey It might be that Dr Li had other, unreported, health conditions that put him at greater risk. Or he may have been exposed to a higher initial dose of the virus that meant he developed more severe symptoms. But it is also worth remembering that seasonal flu mostly kills the young and old, but can kill people in the prime of their life. Is a face mask useful against the virus and how often does it have to be replaced? Tom Lim, Bali, Indonesia There is very little evidence that wearing face masks make a difference. Experts say good hygiene - such as regularly washing your hands and certainly before putting them near your mouth - is vastly more effective. What is the incubation period for the coronavirus? - Gillian Gibs The World Health Organization says the incubation period, which is the time before symptoms appear, ranges from two to 10 days. These estimates will be narrowed down as more data becomes available. Knowing and understanding the incubation period is very important. It allows doctors and health authorities to introduce more effective ways to control the spread of the virus. It means, for instance, that they can introduce more effective quarantine systems, isolating those suspected of carrying the virus from others. Do people who have contracted coronavirus return to full health? - Chris Stepney, Milton Keynes Yes. Many of those who contract coronavirus will experience only mild symptoms. These include fever, coughing and respiratory problems. Most people are expected to make a full recovery. But it can pose a particular risk for elderly people and those with pre-existing problems like diabetes or cancer, or weak immune systems. As of 7 February, Chinese health authorities said that 636 people had died from the virus. The number of confirmed cases stands at 31,198. An expert at China's National Health Commission has said that it can take a week to recovery from mild coronavirus symptoms. Can the coronavirus be transferred through items bought from Wuhan and posted to UK? - Stefan There is no evidence this is a risk. Some diseases - including the coronavirus that causes Sars - can spread through surfaces contaminated by people coughing or sneezing on them. It has not been shown this new coronavirus can do that. Even if it could, there would still be questions about whether international shipping would be a major problem. Cold viruses tend to survive less than 24 hours outside the human body although norovirus (a severe stomach bug) can last months outside the body. The most reassuring fact so far is that cases seem to require close contact with another person - say, a family member or healthcare worker - in order to spread. Is there any reason such viruses are emerging more from China? - Gautam Yes - large populations of people living in close proximity to animals. This coronavirus almost certainly came from an animal source, with one suggestion being snakes. Sars, another coronavirus that originated in China, came from bats and the civet cat. The early cases of this new infection were traced to the South China Seafood Wholesale Market. Live wild animals were also sold including chickens, bats and snakes. Is it possible to vaccinate in order to prevent this respiratory illness? - Hans Friedrich At the moment, there is no vaccine that can protect people against this type of coronavirus, but researchers are looking to develop one. It is a new strain that hasn't been seen in humans before, which means doctors still have lots to learn about it.