In this article, we analyze the emergence of a global security norm of the COVID-19 epidemic as a threat to international security. This crisis is one of the gravest crises that humanity has experienced since the end of World War II in terms of the number of people infected and died, but also in terms of the economic consequences. Here, we provide a framework for understanding the securitization of the COVID-19 epidemic as an international norm defined and promoted by the World Health Organization as a norm entrepreneur, and cascaded down to the level of member states. We identify the actors who developed the main strategic prescriptions of the security norm and the international mechanisms that promoted the cascading of its contents throughout the international system. We further develop the notion of primary and secondary norms, which explain the striking differences amongst industrialized states with regard to the contents, scope, and implementation timeline of the various measures aiming to curb the spread of the virus.