Tim Harford reports on what we know and don't know about the Oxford/Astra Zeneca Covid 19 vaccine, as well as answering questions from both the audience and our editor. On this week's panel of experts is Danny Altman, Professor of Immunology at Imperial College London, Jennifer Rogers, Head of Statistical Research and Consultancy at Phastar and Natasha Loder, Health and Policy Editor at the Economist.