According to Callard and Perego (2021), “Long Covid has a strong claim to be considered the first illness to be collectively made by patients finding one another through Twitter and other social media.” In the first few months of the pandemic, people with COVID-19 started to report unexpected persistent and fluctuating symptoms, including in people with initially mild disease. By sharing experiences on social media patients were able to identify other people like them. Through this patient activism the condition of Long COVID emerged and continues to be defined. Once people started using the term #longcovid, it developed a momentum and has established a patient movement which advocates in favour of resources, rehabilitation, research and recognition. The patient groups often include those with professional authority including doctors and academics and public figures experiencing Long COVID themselves. In this talk I will share results from a large study in England, REACT-Long COVID, which combines in depth biological research into disease mechanisms with participatory research with patients to refine definitions and define outcomes.