The global number of forced migrants is currently the highest since the Second World War [1]. This is a major concern to public health: lack of access to safe water, food, sanitation, and inadequate shelter causes substantial increases in all-cause morbidity and mortality in displaced populations [2]. The number of victims due to infectious diseases can be higher than the direct death toll due to violence, even in particularly brutal conflicts such as the 2003 genocide in Sudan’s Darfur region [3].

However, the true extent of the problem is poorly documented, as there is no systematic health data collection in forced migrants. Deaths often take place beyond the reach of standard health data sources and therefore slip through the net of vital registration systems or large nation-wide health surveys, a key public health resource in developing countries. Disturbingly, the evidence is weakest for the most vulnerable populations, such as internally displaced persons (IDPs), who are displaced within their home country but do not benefit from the same international protection rights and support as refugees do. For instance, researchers were unable to include IDPs in recent national surveys in Colombia and Ethiopia because of security concerns [4,5].