We describe a case of a 24-year-old Brazilian woman previously vaccinated with CoronaVac and a booster dose of Pfizer-BioNTech, with mild-to-moderate COVID-19, with persistent viral shedding. We evaluated viral load, antibody dynamics for SARS-CoV-2 and performed genomic analysis to identify the viral variant. The female remained positive for 40 days following symptom onset (cycle quantification mean: 32.54 ± 2.29). The humoral response was characterized by absence of IgM for the viral spike protein, increased IgG for the viral spike (1800.60 to 19558.60 AU/mL) and for the nucleocapsid (from 0.03 to 8.9 index value) proteins, and high titers of neutralizing antibodies (>488.00 IU/mL). The variant identified was the sublineage BA. 5.1. of Omicron (B.1.1.529). Our results suggest that even though the female produced an antibody response against SARS-CoV-2, the persistent infection can be explained by antibody decline and/or the immune evasion by the Omicron variant, illustrating the need to revaccinate or update vaccines.