In his evidence to the Science and Technology Committee during the early weeks of the pandemic, on 25 March, the Editor of the Lancet expressed concern that mathematical modelling was playing too influential a role in UK scientific advice.157 The prominence of modelling and projections was, and still remains, an important part of the UK’s response to covid-19. Models can be useful and informative to policymakers, but they come with limitations. As Professor Neil Ferguson told the Science and Technology Committee in June 2020, “Models can only be as reliable as the data that is feeding into them.”158 However, we know that—especially in the early stages of the pandemic—there was an acute shortage of good data.159 There was also a limited understanding of the virus early in the pandemic. Key questions, such as the length of immunity conferred by infection, were unknown and hampered accurate modelling.160