More than 688,000 Rohingya refugees have arrived in Cox's Bazar, a district in southeast Bangladesh, since late August 2017, after fleeing violence in Rakhine State, Myanmar. In December, cases of diphtheria emerged in the area. With the last major outbreak happening decades ago, most MSF staff had only ever seen diphtheria in textbooks. MSF has treated since then more than 4,280 people for diphtheria at its medical facilities and helped to vaccinate thousands of others. This web-clip explains the complexity of the process.