Thompson R.N.Bansal S.Clapham H.Dyson L.Gutierrez M.A.Hadley L.Hart W.S.Heesterbeek H.Hollingsworth T.D.House T.Howerton E.Isham V.Lessler J.Leung K.Li X.McBryde E.McCaw J.M.Mollison D.Pan-Ngum W.Parag K.Pellis L.Scarabel F.Swallow B.Thumbi S.M.Tran-Kiem C.Viboud C.Plank M.J.Mahidol University2026-02-072026-02-072026-01-28Proceedings of the Royal Society B Biological Sciences Vol.293 No.2063 (2026)https://repository.li.mahidol.ac.th/handle/123456789/114862Early in an infectious disease outbreak, key policy questions include whether and how the outbreak can be brought under control. In the epidemiological modelling literature, analyses of outbreak controllability have often focused on metrics such as reproduction numbers (which quantify the number of infections generated by each infected individual). However, whether an outbreak can be controlled is a complex question, depending on both the precise definition of 'under control' used and numerous factors affecting decision-makers' ability to implement transmission-reducing measures. Here, based on discussions at the Isaac Newton Institute's 'Modelling and inference for pandemic preparedness' programme (5-30 August 2024), we describe a wide range of factors affecting outbreak controllability in practice. Programme participants came from institutions in ten countries, enabling discussions to reflect experiences of using models to inform policy in different settings. We divide the factors according to whether they relate predominantly to characteristics of the pathogen, host population or available interventions, and describe policy considerations when assessing whether an outbreak is controllable.Environmental ScienceBiochemistry, Genetics and Molecular BiologyAgricultural and Biological SciencesMedicineImmunology and MicrobiologyArticleSCOPUS10.1098/rspb.2025.28482-s2.0-1050288136481471295441592768