In 2014 the World Health Organization (WHO) was widely criticised for failing to anticipate that an outbreak of Ebola in a remote forested region of south-eastern Guinea would trigger a public health emergency of international concern (pheic). In explaining the WHO's failure, critics have pointed to structural restraints on the United Nations organisation and a leadership vacuum' in Geneva, among other factors. This paper takes a different approach. Drawing on internal WHO documents and interviews with key actors in the epidemic response, I argue that the WHO's failure is better understood as a consequence of Ebola's shifting medical identity and of triage systems for managing emerging infectious disease (EID) risks. Focusing on the discursive and non-discursive practices that produced Ebola as a problem' for global health security, I argue that by 2014 Ebola was no longer regarded as a paradigmatic EID and potential biothreat so much as a neglected tropical disease. The result was to relegate Ebola to the fringes of biosecurity concerns just at the moment when the virus was crossing international borders in West Africa and triggering large urban outbreaks for the first time. Ebola's fluctuating medical identity also helps explain the prominence of fear and rumours during the epidemic and social resistance to Ebola control measures. Contrasting the WHO's delay over declaring a pheic in 2014, with its rapid declaration of pheics in relation to H1N1 swine flu in 2009 and polio in 2014, I conclude that such missed alarms' may be an inescapable consequence of pandemic preparedness systems that seek to rationalise responses to the emergence of new diseases.