[The Conversation Africa] This week the University of Oxford and Astra Zeneca temporarily postponed further vaccination in clinical trials of the COVID-19 candidate vaccine, AZD1222, after one of the participants fell ill. There are more than 15,000 participants already enrolled across multiple studies of the vaccine in several countries around the world, including 1,800 in South Africa. The Conversation Africa's health and medicine editor, Ina Skosana, asked Professor Shabir Madhi, who is leading the South African leg of the trial