Virological and serological characterization of critically ill patients with COVID-19 in the UK: interactions of viral load, antibody status and B.1.1.7 variant infection by Ratcliff, J, Nguyen, D, Fish, M, Rynne, J, Jennings, A, Williams, S, Al-Beidh, F, Bonsall, D, Evans, A, Golubchik, T, Gordon, AC, Lamikanra, A, Tsang, P, Ciccone, NA, Leuscher, U, Slack, W, Laing, E, Mouncey, PR, Ziyenge, S, Oliveira, M, Ploeg, R, Rowan, KM, Shankar-Hari, M, Roberts, DJ, Menon, DK, Estcourt, L, Simmonds, P, Harvala, H