Neurological symptoms can occur after COVID-19 mRNA vaccination. However, its etiology hasn't been fully revealed.

Patient 1 presented with headache, low-grade fever and memory disturbance (Day 3). Intravenous acyclovir and meropenem were administered under a possible diagnosis of aseptic meningitis but not effective. Patient 2 presented with visual disturbance, headache, dysarthria, a left forearm tremor, dysesthesia of the mouth and distal limbs, and visual agnosia (Day 10). In both patients, reverse transcription polymerase chain reaction test results for severe acute respiratory syndrome coronavirus 2 were negative. Complete blood cell count, blood-chemistry including electrolytes and antibody titers, and cerebrospinal fluid test findings were unremarkable initially. However, second cerebrospinal fluid test of Patient 1 (Day 8) showed pleocytosis (942 cells/µL, normal ? 5 cells/µL) and elevated protein levels (181 mg/dL, normal 10–40 mg/dL). Brain MRI on Day 17 in Patient 1 and Day 15 in Patient 2 after receiving the vaccination showed high signal intensity lesions at the midline of the splenium of the corpus callosum. Based on the typical imaging features, the patients were diagnosed with MERS. Intravenous methylprednisolone therapy (1,000 mg/day for 3 days) improved their symptoms and MRI lesion disappeared.