Commentary on the use of the reproduction number R during the COVID-19 pandemic by Vegvari, C, Abbott, S, Ball, F, Brooks-Pollock, E, Challen, R, Collyer, BS, Dangerfield, C, Gog, JR, Gostic, KM, Heffernan, JM, Hollingsworth, TD, Isham, V, Kenah, E, Mollison, D, Panovska-Griffiths, J, Pellis, L, Roberts, MG, Scalia Tomba, G, Thompson, RN, Trapman, P