Features of Systemic Immune Response From COVID-19 Vaccination on 18F-FDG PET/CT.

The rapid rollout of COVID-19 vaccination is accompanied by incidental findings on 18F-FDG PET/CT. Most cases describe reactive axillary lymphadenopathy. A 46-year-old woman with previous history of stage 3A breast cancer underwent follow-up 18F-FDG PET/CT, which demonstrated avid left axillary nodes and intense diffuse splenic uptake and moderate diffuse bone marrow uptake. She had been administered COVID-19 vaccination in the left deltoid 1 week earlier and required hospitalization for 24 hours due to fever. Symptoms settled with supportive treatment. One month after the PET/CT scan, she remained well. Sites of uptake were taken to relate to a systemic immune response.