Abstract Background It is currently unclear whether severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reinfection will remain a rare event, only occurring in individuals who fail to mount an effective immune response, or whether it will occur more frequently when humoral immunity wanes following primary infection. Methods A case of reinfection was observed in a Belgian nosocomial outbreak involving 3 patients and 2 healthcare workers. To distinguish reinfection from persistent infection and detect potential transmission clusters, whole genome sequencing was performed on nasopharyngeal swabs of all individuals including the reinfection case’s first episode. Immunoglobulin A, immunoglobulin M, and immunoglobulin G (IgG) and neutralizing antibody responses were quantified in serum of all individuals, and viral infectiousness was measured in the swabs of the reinfection case. Results Reinfection was confirmed in a young, immunocompetent healthcare worker as viral genomes derived from the first and second episode belonged to different SARS-CoV-2 clades. The symptomatic reinfection occurred after an interval of 185 days, despite the development of an effective humoral immune response following symptomatic primary infection. The second episode, however, was milder and characterized by a fast rise in serum IgG and neutralizing antibodies. Although contact tracing and viral culture remained inconclusive, the healthcare worker formed a transmission cluster with 3 patients and showed evidence of virus replication but not of neutralizing antibodies in her nasopharyngeal swabs. Conclusions If this case is representative of most patients with coronavirus disease 2019, long-lived protective immunity against SARS-CoV-2 after primary infection might not be likely.