Illustrated by a clinical case supplemented by epidemiologic data, early reinfections with SARS-CoV-2 Omicron BA.1 after infection with Delta variant, and reinfection with Omicron BA.2 after Omicron BA.1 infection, can occur within 60 days, especially in young, unvaccinated persons. The case definition of reinfection, which influences retesting policies, should be reconsidered.
Keywords: Belgium; COVID-19; SARS-CoV-2; coronavirus disease; epidemiology; reinfections; respiratory infections; severe acute respiratory syndrome coronavirus 2; testing policies; vaccination; viruses; zoonoses.