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Vaccination against COVID-19 is happening worldwide, with most vaccines requiring 2 doses to reach its maximum potential. It is the most efficient measure to prevent new cases of COVID-19, both of infection and reinfection. This case reports the reinfection of a female receptionist at an urgent care facility, where the research group was testing and monitoring symptoms of patients with flu syndrome, in the city of Belo Horizonte, Minas Gerais, Brasil, where she reinfected between the two preconized doses. Her initial infection occurred in September 2020 and reinfection in February 2021, 14 days after the first dose - both confirmed by RT-PCR - with reportedly worse symptoms on the latter. We warn for the possibility of reinfection episodes even after the first dose of vaccination, differently from what literature stated so far, so that health agents can organize more effective security measures, in a context of viral mutation and of new strains.

The left atrial appendage (LAA) is an extension of the left atrium (LA) and has complex anatomical structure and unique pathophysiological properties. The LAA functions as a decompression chamber during left ventricular (LV) systole and under increased left atrial pressure conditions. Despite previously being considered a relatively insignificant portion of the cardiac anatomy, the LAA has been highlighted as an important structure involved in the genesis of thrombus formation and thromboembolic events. With the recent development of percutaneous closure devices, LAA morphology assessments have become increasingly important. This article aims to describe LAA anatomy and morphology, function assessment parameters, thrombus diagnostic challenges, and the main imaging modalities, particularly transesophageal echocardiography.