Multisystem inflammatory syndrome in a fully vaccinated 18-year-old without known SARS-CoV-2 infection

BACKGROUND: Multisystem inflammatory syndrome in children (MIS-C) is a febrile syndrome that is observed in the pediatric population following severe acute respiratory syndrome 2 (SARS-CoV-2) infection. Vaccines have prevented or lessened the severity of the initial acute respiratory infection, while their effectiveness against severe MIS-C is just beginning to be reported. CASE PRESENTATION: Here we report a fully vaccinated teenage female with no known history of SARS-CoV-2 infection who presented with shock and heart failure. Her presentation was initially thought secondary to a retropharyngeal abscess but was later identified as MIS-C after confirmed nucleocapsid antibody. CONCLUSIONS: Given the recent Omicron waves, the ongoing international outbreaks with evolving variants and the continued evolution of the COVID-19 pandemic, this case emphasizes the need to include MIS-C in the differential diagnosis, even in a fully vaccinated, previously healthy child.