The WHO’s fragmented structure and organisational sub-cultures can be invoked to explain why different units within the WHO act according to their own preferences, leading to agency slack and an inability of the WHO to meet its mandate.The WHO has advanced a global health security narrative in response to disease outbreaks and that this fits some principals’ interests and not those of others. It can be distinguished between the WHO’s relationship with ‘proximal principals’, which the WHO deems critical to its mission, and its relationship with ‘distal principals’, which are not.