Over the past 18 months, the largest-ever recorded avian influenza outbreak has decimated bird populations around the world. But recently bird flu has spread to mammals. Last week, Peru reported the deaths of 585 sea lions. If the virus has mutated to enable mammal-to-mammal transmission, that could be an intermediate step towards human-to-human transmission. How worrying is this threat? Susan Davies, CEO of the Scottish Seabird Centre, describes how the H5N1 avian flu has affected populations of wild birds. Ian Brown of Britain’s Animal and Plant Health Agency explains why the dynamics of this outbreak are concerning scientists. Plus, we ask Marion Koopmans, head of viroscience at Erasmus MC, why she’s more worried than ever about a human influenza pandemic. The Economist’s Slavea Chankova also compares the influenza threat to the covid-19 pandemic. Do we have enough tools in our arsenal? Alok Jha hosts.  For full access to The Economist’s print, digital and audio editions subscribe at economist.com/podcastoffer and sign up for our weekly science newsletter at economist.com/simplyscience. Hosted on Acast. See acast.com/privacy for more information.