Episode description

Tim Harford is an economist not an immunologist, so he's on solid ground with this week’s programme which is all about numbers. Some of them are small but significant: 7 reported cases of cerebral venous thrombosis in Germany. Others are huge: 400 million doses of Covid 19 vaccine administered around the world. Then there are the numbers that we’d love to know but don’t - about the effectiveness of a single dose, or whether we are getting closer to herd immunity. We find out what the numbers can tell us about Covid 19 vaccinations with this week's panel of guests: Professor Sheena Cruickshank, of the University of Manchester, Professor Susan Ellenberg, from the University of Pennsylvania and Professor Sir David Spiegelhalter of the University of Cambridge

Producers: Sandra Kanthal and Beth Sagar-Fenton

Listener questions can be sent to: vaccine@bbc.co.uk