Predictors of Long-Term Evolution in Long COVID; 4-Year Follow-Up. (BioICOPER Follow-up Study)

The study includes a citizen participation component through the IBSAL Citizen Committee for review and dissemination of results. A prospective observational cohort study following 400 adults with a confirmed diagnosis of long COVID, previously enrolled in the BioICOPER baseline study. Participants will undergo reevaluation four years after their initial inclusion, assessing: * Clinical symptoms (fatigue, dyspnea, sleep, cognition, nutrition, frailty). * Lifestyle factors (physical activity, diet, alcohol and tobacco use). * Vascular structure and function using carotid ultrasound, pulse wave velocity (SphygmoCor®, Vasera®), and retinal imaging. * Proteomic profiling and quantification of SARS-CoV-2 N and S proteins using ELISA and mass spectrometry. * Predictive modeling using artificial intelligence (AI) and bioinformatics methods (ESALAB group). The study will identify biological, vascular, and behavioral determinants of long COVID progression, aiming to build predictive models to support personalized medicine.