As the northern hemisphere heads into autumn and winter, cold and flu are beginning to spread and more people find themselves with coughs, fevers and a runny nose. With Covid-19, this brings new challenges. Should we quarantine at the first sign of the sniffles? Could co-infections of flu and Covid-19 make your symptoms worse? Do we have the capacity to test for more than one virus? In part 2 of our investigation into what happens when flu season hits, Ian Sample speaks to Prof Peter Horby about what it might mean for both individuals and medical professionals if multiple respiratory viruses are circulating, and how we can best prepare for a potential winter resurgence of Covid-19. Help support our independent journalism at theguardian.com/sciencepod