Prolonged generalized immune response on ¹⁸F-FDG PET/CT following COVID-19 vaccination

The Coronavirus disease 2019 (COVID-19) pandemic continues to be a major public health concern affecting millions of people globally. The COVID-19 vaccination has implications in medical assessment of cancer patients especially undergoing diagnostic imaging such as ¹⁸F-fluoro-deoxyglucose (FDG) positron emission tomography with computed tomography (PET/CT). The inflammatory changes following vaccination can cause false positive findings on imaging. We present a case of a patient with esophageal carcinoma who had ¹⁸F-FDG PET/CT scan, 8 weeks following booster dose of Moderna COVID-19 vaccination, which showed widespread FDG avid reactive lymph nodes and intense splenic uptake for prolonged duration of approximately 8 months (34 weeks) probably representing generalized immune response. It is important from radiological/nuclear medicine perspective to recognize imaging features of such rare effect of COVID-19 vaccination, which can pose a challenge in assessing ¹⁸F-FDG PET/CT scans in cancer patients. It has also opened new avenues for future research evaluating such COVID-19 vaccine-related prolonged systemic immunological response in cancer patients.