Efficacy of the ChAdOx1 nCoV-19 Covid-19 vaccine against the B.1.351 variant by Madhi, SA, Baillie, V, Cutland, CL, Voysey, M, Koen, AL, Fairlie, L, Padayachee, SD, Dheda, K, Barnabas, SL, Bhorat, QE, Briner, C, Kwatra, G, Ahmed, K, Aley, P, Bhikha, S, Bhiman, JN, Bhorat, AE, du Plessis, J, Esmail, A, Groenewald, M, Horne, E, Hwa, S-H, Jose, A, Lambe, T, Laubscher, M, Malahleha, M, Masenya, M, Masilela, M, McKenzie, S, Molapo, K, Moultrie, A, Oelofse, S, Patel, F, Pillay, S, Rhead, S, Rodel, H, Rossouw, L, Taoushanis, C, Tegally, H, Thombrayil, A, van Eck, S, Wibmer, CK, Durham, NM, Kelly, EJ, Villafana, TL, Gilbert, S, Pollard, AJ, de Oliveira, T, Moore, PL, Sigal, A, Izu, A