The number of suspected diphtheria cases among the Rohingya refugees in Cox's Bazaar has increased to 549, with nine confirmed deaths as of 11 December. The extremely congested conditions in the camps, low immunization coverage of the refugees, the lack of clean water and proper sanitation facilities are conducive to a rapid spread of the epidemic, with the number of cases expected to double every three to five days. The estimated peak time will be around the New Year. WHO and health partners have triggered alert level three and established a diphtheria task force in Cox's Bazaar to coordinate case management, vaccination, logistics, contact tracing and lab capacity. An ongoing vaccination campaign is targeting children under five years old. Most of the available emergency health facilities and reception centres are being converted to increase bed capacity and isolation, but many gaps still remain.