Features of 20 133 UK patients in hospital with covid-19 using the ISARIC WHO Clinical Characterisation Protocol: prospective observational cohort study by Docherty, AB, Harrison, EW, Green, CA, Hardwick, HE, Pius, R, Norman, L, Holden, KA, Read, JM, Dondelinger, F, Carson, G, Merson, L, Lee, J, Plotkin, D, Sigfrid, L, Halpin, S, Jackson, C, Gamble, C, Horby, PW, Nguyen-Van-Tam, JS, Ho, A, Russell, CD, Dunning, J, Openshaw, PJ, Baillie, JK, Semple, MG, ISARIC4C investigators