Long COVID (LC) affects an estimated 5-10% of individuals with SARS-CoV-2 causing a persistent physical, cognitive, and functional impairment with potentially severe socioeconomic consequences. While RECOVER-Adult cycle 1 established the largest, most comprehensive U.S. adult LC cohort (14,730 participants), key questions remain about long-term disease trajectories, biological mechanisms, and late-emerging complications. RECOVER-Adult cycle 2 will follow selected participants for two years each, focusing on neurocognitive, cardiopulmonary and infection-associated chronic conditions (IACC) such as Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) and autonomic dysfunction. Using a case-cohort design, the study will investigate disease persistence versus resolution, biological mechanisms, and onset of new chronic illnesses, generating critical insights to guide prevention, treatment, and public health policy.