Since May 2015, an outbreak of the Middle East respiratory syndrome coronavirus has affected South Korea. The virus, which causes Middle East Respiratory Syndrome (MERS), is a newly emerged betacoronavirus that was first identified in a patient from Saudi Arabia in April 2012.Experts from the World Health Organization who have dealt with MERS are coming to South Korea to assess the pattern of the virus spread and to look at public health response efforts. The outbreak in South Korea has been the largest outside Saudi Arabia — where the virus was discovered.