cerebral venous sinus thrombosis; This spontaneous case was reported by a consumer and describes the occurrence of CEREBRAL VENOUS SINUS THROMBOSIS (cerebral venous sinus thrombosis) in a 48-year-old female patient who received mRNA-1273.815 (SPIKEVAX 2023-2024) (batch no. ASKU) for COVID-19 prophylaxis.     Patient reported that she had no history of clotting issues nor family history. The patient also took Tylenol or Ibuprofen. Patient had no known allergies.  The patient's past medical history included COVID-19 (Her symptoms were sore throat cough, fever, chest congestion, sneezing a lot a, and felt stuffy in the nose.) in January 2022 and Vertigo (unusual episode over the summer 2023, was not able to stay upright like room was pulling to one side, Felt like gravity was pulling her, had to hold wall to walk , she had to walk on the outside by closet and push myself from wall to get my bed. had 3-4 episodes like this in July 2023) in 2023. Previously administered products included for COVID-19 vaccination: Pfizer (Dose 1, LOT : EL0142) on 05-Jan-2021, Pfizer (Dose 2, LOT : EL3248) on 26-Jan-2021, Pfizer Bivalent (Dose 3 and LOT: GH9702) on 17-Sep-2022; for COVID-19 prophylaxis: Moderna Vaccine (Dose 4 and LOT: 051F21A) on 04-Nov-2021; for Product used for unknown indication: Flu vaccine. Past adverse reactions to the above products included No adverse event with Flu vaccine, Moderna Vaccine, Pfizer, Pfizer and Pfizer Bivalent. Concurrent medical conditions included Migraine. Concomitant products included BOTULINUM TOXIN TYPE A (BOTOX), DICLOFENAC POTASSIUM (CAMBIA) and UBROGEPANT (UBRELVY) for an unknown indication.    On 19-Oct-2023, the patient received fifth dose of mRNA-1273.815 (SPIKEVAX 2023-2024) (unknown route) 1 dosage form. In 2023, the patient experienced CEREBRAL VENOUS SINUS THROMBOSIS (cerebral venous sinus thrombosis) (seriousness criterion medically significant). At the time of the report, CEREBRAL VENOUS SINUS THROMBOSIS (cerebral venous sinus thrombosis) had not resolved.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): In 2023, Magnetic resonance imaging head: Cerebral Venous Sinus Thrombosis (CVST). On 23-Oct-2023, C-reactive protein: elevated. On 23-Oct-2023, Factor VIII activity test: elevated.     For mRNA-1273.815 (SPIKEVAX 2023-2024) (Unknown), the reporter did not provide any causality assessments.   On an unspecified date, an Angiogram and Venogram to ensure adequate blood flow. The patient stated that she didn't have a stroke, they wanted to rule out. Blood clot was recanalizing.  Treatment medication was not reported. Company comment This spontaneous case concerns a 48-year-old female patient, with medical history of Vertigo (had 3-4 episodes about 3 months before the vaccine), who experienced the unexpected, serious (medically significant) AESI of Cerebral venous sinus thrombosis which occurred the same year that the fifth dose of mRNA-1273.815 (SPIKEVAX 2023-2024) was administered. Previously, the patient received 3 doses of Pfizer COVID-19 vaccine and 1 Bivalent. It was reported that a magnetic resonance imaging head revealed Cerebral Venous Sinus Thrombosis (CVST). C-reactive protein and factor VIII activity test were elevated. An Angiogram and Venogram were performed to ensure adequate blood flow. The patient stated that she didn't have a stroke, they wanted to rule out. Blood clot was recanalizing. No further clinical information was provided for medical review. The medical history of Vertigo could be a confounder for the event. The benefit-risk relationship of mRNA-1273.815 (SPIKEVAX 2023-2024) vaccine is not affected by this report.