EC Clinical and Medical Case Reports

Acute encephalopathy after mRNA-based COVID-19 vaccination has been infrequently reported, however, there were no reports with confirmed pathogen. We here report a case diagnosed with herpes simplex virus encephalitis (HSE) after mRNA-1273 (Moderna COVID-19 vaccine) vaccination. We described the clinical presentation, laboratory and imaging findings, and treatment of a 52-year-old woman. The patient presented with symptoms of encephalopathy beginning two days after a dose of mRNA-1273. Cerebrospinal fluid analysis showed mild pleocytosis and elevated protein level. Brain MRI showed T2 hyperintensity in the left medial temporal lobe. Polymerase chain reaction multiplex test confirmed positive test for herpes simplex virus-1. Her symptoms gradually improved with the treatment of intravenous acyclovir. Although rare, HSE can occur in people with mRNA-based COVID-19 vaccination and should be considered in the setting of acute or subacute encephalopathy after vaccination.

 Keywords: Herpes Simplex Virus Encephalitis; COVID-19 Vaccine; mRNA Vaccine

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