This research explores the question, why does the level of international cooperation vary in the international response to pandemics? The research presents an analytical model to analyse the differences among the levels of international cooperation in four disease outbreaks: Influenza H1N1 in 2009, MERS-CoV in 2012, Ebola in 2013-2016 and Zika in 2013-2016. The model introduces sixteen indicators categorized in four main areas: i) international participation; ii) international assistance; iii) scientific response and; iv) policy convergence. These indicators facilitate comparison across cases and show that Influenza H1N1 had a high level of cooperation; MERS-CoV a low-medium level; Ebola a low-medium level; and Zika a high level. This study applies the theory of epistemic communities developed by Peter Haas to explain variation in the level of cooperation in global health. The research identifies an epistemic community for each case and examines three general characteristics underlined in Haas' theory: a) the creation of consensual knowledge; b) the dissemination of knowledge to the policymakers and; c) the institutionalization of bureaucratic power. This research shows that these characteristics are present in all epistemic communities, but their quality varies from one community to another and influences cooperation. While some epistemic communities created consensual knowledge and a clear policy goal, they were unable to disseminate their knowledge to relevant policymakers, and thus had limited bureaucratic power. Other epistemic communities established consensual knowledge, disseminated it to key policy makers and therefore exhibited enough bureaucratic power to influence the policy-making process. The proposed framework presents a comprehensive and simplified model that measures these characteristics. The findings show that in the absence of a clear consensus regarding the nature of the problem and possible solutions among members of the epistemic community; the inability to disseminate this consensual knowledge to policymakers; and the building of bureaucratic power through their participation in crucial parts of the process; the ability to influence global health governance towards cooperative outcomes is diminished.