Tens of of people have been sickened by a new coronavirus, called 2019-nCoV, in at least 25 countries, including the US. Coronaviruses attack the respiratory system, sometimes targeting the cells deep within the lungs. Only seven, including 2019-nCoV, SARS, and MERS, have evolved to infect humans.
The outbreak was first reported to the World Health Organization by Chinese officials on December 31 in Wuhan, a city of 11 million in Hubei province. By mid-January, it had begun spreading rapidly.
On January 23, quarantine measures expanded from Wuhan to two additional cities about 50 miles east of Wuhan — Huanggang and Ezhou — effectively stifling the movement of nearly 20 million people. It later expanded further to cover over 50 million people. The World Health Organization has ruled that the outbreak is a global health emergency, a rare designation the agency gives outbreaks that pose an international risk.
There are still many unknowns about this outbreak. Experts still aren’t sure which animal carries this virus and transmitted it to humans, how easily it spreads among people, or how deadly it is.