A Transient Inflammatory Reaction with a B-Cell Lymphoid Infiltrate and Dysplastic Bone Marrow Changes Associated with the BNT162b2 COVID-19 Vaccine

COVID-19 vaccines were introduced soon after the COVID-19 pandemic emerged in 2020. Various side effects were reported worldwide, including several types of common systemic side effects such as fever and general fatigue. Reports of other rare manifestations also emerged. We report the case of an adult male with a rare systemic syndrome mimicking lymphoma after he had received the first dose of an mRNA-based COVID-19 vaccine. After nearly 6 months of investigation with suspicion for an infection or malignancy, all symptoms resolved, laboratory tests normalized, and imaging showed no sign of active disease. LEARNING POINTS: A lymphoma-like reaction is a possible side effect of COVID-19 vaccination. It is important to rule out other causes of systemic symptoms before diagnosing a reaction to a COVID-19 vaccine. A lymphoma-like reaction following administration of a COVID-19 vaccine has a good prognosis.