Six Years of COVID-19: Lessons from Epidemiology, Vaccination Campaigns, Clinical Risk Stratification, and Thromboembolic Surveillance.

Six years after the emergence of SARS-CoV-2, COVID-19 remains a dynamic public health challenge shaped by viral evolution, heterogeneous population immunity, changing vaccine strategies, and the long-term consequences of acute infection. Although the transition from pandemic emergency to endemic circulation has reduced the global burden of severe disease, COVID-19 continues to affect vulnerable populations, particularly older adults, frail patients, immunocompromised individuals, and subjects with multiple comorbidities. Vaccination has substantially modified the clinical course of infection, reducing hospitalization, intensive care admission, and mortality, while also reshaping surveillance priorities toward variant monitoring, vaccine effectiveness, waning immunity, breakthrough infections, and long COVID. At the same time, the pandemic has highlighted the need for integrated clinical risk stratification, including age, sex, frailty, inflammatory biomarkers, respiratory support requirements, and thromboembolic risk. Venous and arterial thrombotic complications have represented a key feature of severe COVID-19 and remain relevant for both acute management and post-discharge follow-up. This narrative review summarizes the main lessons learned from six years of COVID-19, focusing on epidemiology, vaccination campaigns, clinical risk assessment, thromboembolic complications, and surveillance strategies. Particular attention is given to the need for multidisciplinary and data-driven approaches capable of integrating virological, epidemiological, clinical, geriatric, and vascular medicine perspectives. Future COVID-19 surveillance should move beyond case counting and incorporate vaccine impact, population vulnerability, thrombotic and bleeding complications, long-term outcomes, and preparedness for emerging variants.