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COVID-19 has brought to the forefront a group of network engineers specialized in epidemiological modelling. Two questions about this speciality arise here. How are their models built and what does their irruption into the debate in recent months encompass? How have these physicists and mathematicians managed to become epidemiological experts without a background in the health profession? The present article considers such questions by examining the models produced by this specialty, as well as the process of its emergence and the division of labour within it. The final section of the analysis looks back at the first wave of the epidemic and at the debates that it reinforced or opened up in relation to this new specialty. The article is based on a field survey conducted in four computational epidemiology laboratories based in Paris, Turin, Boston and Los Alamos.