Key questions for modelling COVID-19 exit strategies by Thompson, RN, Hollingsworth, TD, Isham, V, Arribas-Bel, D, Ashby, B, Britton, T, Challoner, P, Chappell, LHK, Clapham, H, Cunniffe, NJ, Dawid, AP, Donnelly, CA, Eggo, R, Funk, S, Gilbert, N, Glendinning, P, Gog, JR, Hart, WS, Heesterbeek, H, House, T, Keeling, M, Kiss, IZ, Kretzschmar, M, Lloyd, AL, McBryde, ES, McCaw, JM, McKinley, TJ, Miller, JC, Morris, M, ONeill, PD, Parag, KV, Pearson, CAB, Pellis, L, Pulliam, JRC, Ross, JV, Tomba, GS, Silverman, BW, Struchiner, CJ, Tildesley, MJ, Trapman, P, Webb, CR, Mollison, D, Restif, O