Extreme fatigue, brain fog, sleep disturbances, chest pain and skin rashes. These are just a few of the on-going symptoms of long Covid, a disorder that can persist for many months after an initial Covid infection. With such a vast range of symptoms, and health organisations stretched to capacity by the acute stage of the disease, long Covid has continued to remain something of a mystery. But with numerous studies trying to understand what exactly people are suffering from, progress is being made. Ian Sample speaks to Prof Akiko Iwasaki about what we do and don’t know about long Covid, and how the vaccine could reveal clues about what’s behind the disorder. Help support our independent journalism at https://www.theguardian.com/sciencepod">theguardian.com/sciencepod