Although several countries around the world continue to have high rates of Covid-19 infections, including the UK and US, many of their citizens are yet to be infected with the Sars-Cov-2 virus. This includes countless individuals who have knowingly been exposed, often multiple times, but have still never had a positive test. Madeleine Finlay speaks to Linda Geddes about how scientists are trying to solve the mystery of why some people seemingly don’t catch Covid, and what could be behind this phenomenon. Help support our independent journalism at https://www.theguardian.com/sciencepod">theguardian.com/sciencepod