According to the World Health Organisation, 16-21% of people with the virus in China became severely ill and 2-3% of those infected have died.
A key factor that influences transmission is whether the virus can spread in the absence of symptoms – either during the incubation period (the days before people become visibly ill) or in people who never get sick.
On Sunday, Chinese officials said transmission had occurred during the incubation period.
Dr Sadia Shinwari got a short video about which symptoms or signs we expect and how to protect ourselves.