One of the most promising COVID-19 vaccine trials has been halted; after one of its U.K participants developed a “potentially unexplained illness”. The vaccine was developed by the University of Oxford in partnership with AstraZeneca, and is currently being trialled in South Africa, Brazil, the UK and the US. Shabir Madhi, Professor of Vaccinology at the University of Witwatersrand joins CNBC Africa for more.