Seven people have died so far, but we know from outbreaks elsewhere that the virus is lethal in around 37 per cent of cases.
So far MERS remains a hospital-transmitted infection: nasty and expensive to treat, but in theory manageable. On Tuesday, the South Korean health ministry announced that it expects the outbreak to start declining this week. And a genetic analysis shows MERS is showing no signs of going pandemic – yet.
That doesn't mean it isn't seeing the world. Since the virus emerged in 2012, it has invaded 25 countries. But the vast majority of the 1190 known cases have been in Saudi Arabia and its neighbours. The first South Korean case was in a man who had visited Saudi Arabia, the UAE, Bahrain and Qatar.
South Korea is the first country outside the Middle East with more than a few cases, or where the virus has transmitted between three people in succession. The spike in cases this week is that third wave of people, who were exposed a week or more ago.