Airborne transmission is one of the main ways that SARS-CoV-2 spreads. So why has it taken so long to be officially recognised? Host Kenneth Cukier and science correspondent Alok Jha investigate the flaws in public-health guidelines and how to assess the risk of aerosol contagion. It is time for a revolution in ventilation. For full access to The Economist’s print, digital and audio editions subscribe at economist.com/podcastoffer and sign up for our new weekly science newsletter at economist.com/simplyscience.   See acast.com/privacy for privacy and opt-out information.