Prodromal, asymptomatic and afebrile infections cannot be detected by temperature measurement, one of the main components of border control, whether by thermal scanning or by core temperature measurement of symptomatic travellers [23] . Moreover, the proportion of afebrile or asymptomatic people is likely to be higher in infected travellers, as more severely unwell people will be less likely to travel. Thermal imaging is therefore even less likely to have been effective at the borders than in other places where more severely ill patients are seen [24] . Indeed, China used intensive thermal screening for pH1N1 at airports and had a positive detection rate of only 14 cases per million passengers screened [25] .