A 54-year-old man who was previously found to be COVID-19 positive received two doses of mRNA-1273 (Moderna) vaccine 4 weeks apart, as recommended by the manufacturer. He was brought to the emergency department 1 day after second dose of the vaccine with altered mental status, headache and high fever. The patient was hospitalised for 2 days and managed with supportive care. He completely recovered with return of mental status to baseline and resolution of fever.