Scientists have proposed several different, yet interconnected, origin stories to explain these wide-ranging symptoms: The coronavirus could damage organs, spawn tiny blood clots, trigger autoimmunity, hide out in tissues or prompt new and ongoing symptoms in other, more subtle ways. To complicate matters further, these narratives are not mutually exclusive: Several could be occurring at the same time in a particular patient, or one could set off another in an unhappy sequence of events that keeps the patient in perpetual bad health. By teasing apart the theories one by one, researchers are gaining a greater understanding of this enigmatic illness and inching closer to therapies that don’t just mask symptoms but eliminate the root cause.