fatigue; muscle pain; headache; nausea; Where the vaccine was given the area of administration was sore and tender.; Patient states that he felt drunk and felt like he got run over by a truck.; weakness; Dizziness; Woke up with chills having to cover up with a blanket.; Fluttering heart rate/fast heart rate; Trouble breathing when walking; Felt hot and went to bed; This spontaneous case was reported by a patient and describes the occurrence of CARDIAC FLUTTER (Fluttering heart rate/fast heart rate) in an adult male patient who received mRNA-1273.815 (SPIKEVAX 2023-2024 PFS) (batch no. 3030371) for COVID-19 prophylaxis. The occurrence of additional non-serious events is detailed below.     The patient's past medical history included Breathing difficult (Patient has a history of breathing issues.), COVID-19 (Diagnosed with Covid-19 3 times.) in September 2020, COVID-19 (Does not remember second covid-19 infection), COVID-19 (third was in June 2022) in June 2022 and CPAP. Previously administered products included for Product used for unknown indication: Flu Shot. Past adverse reactions to the above products included No adverse effect with Flu Shot.    On 25-Sep-2023, the patient received fourth dose of mRNA-1273.815 (SPIKEVAX 2023-2024 PFS) (unknown route) 1 dosage form. On 25-Sep-2023, the patient experienced CARDIAC FLUTTER (Fluttering heart rate/fast heart rate) (seriousness criterion medically significant), DYSPNOEA (Trouble breathing when walking) and FEELING HOT (Felt hot and went to bed). On 26-Sep-2023, the patient experienced FEELING DRUNK (Patient states that he felt drunk and felt like he got run over by a truck.), ASTHENIA (weakness), DIZZINESS (Dizziness) and CHILLS (Woke up with chills having to cover up with a blanket.). On an unknown date, the patient experienced FATIGUE (fatigue), MYALGIA (muscle pain), HEADACHE (headache), NAUSEA (nausea) and VACCINATION SITE PAIN (Where the vaccine was given the area of administration was sore and tender.). At the time of the report, CARDIAC FLUTTER (Fluttering heart rate/fast heart rate), DYSPNOEA (Trouble breathing when walking), FEELING HOT (Felt hot and went to bed), FEELING DRUNK (Patient states that he felt drunk and felt like he got run over by a truck.), ASTHENIA (weakness), DIZZINESS (Dizziness), CHILLS (Woke up with chills having to cover up with a blanket.), FATIGUE (fatigue), MYALGIA (muscle pain), HEADACHE (headache), NAUSEA (nausea) and VACCINATION SITE PAIN (Where the vaccine was given the area of administration was sore and tender.) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On 25-Sep-2023, Heart rate: 81, before vaccine and 109 in evening. On 26-Sep-2023, Heart rate: 114 in morning and 105 in evening. On 27-Sep-2023, Heart rate: 91 in morning and 111 in evening. On 27-Sep-2023, Oxygen saturation: 92 and 93 in the evening. On 28-Sep-2023, Heart rate: 85, Normal. On 28-Sep-2023, Oxygen saturation: 94, 2 readings.     For mRNA-1273.815 (SPIKEVAX 2023-2024 PFS) (Unknown), the reporter did not provide any causality assessments.   Concomitant medication was not provided. Patient received his first Moderna bivalent Covid-19 vaccine as a booster dose on October 12, 2022 with lot number AS714813. Patient had trouble breathing when walking and a fast heartbeat. He also felt hot and went to bed and woke up with chills having to cover up with a blanket when he woke up. He had dizziness and weakness. Patient stated that he felt drunk and felt like he got run over by a truck. The patient has an Oxygen monitor. He does have a history of bad breathing issues and using Oxygen. Patient does not currently use Oxygen. Patient does also use a CPAP machine. On Sep 28, 2023 patient reports feeling better with a pulse of 85. Earlier in the week the patient's pulse was elevated. Patient had fluttering heart rate, fatigue, muscle pain, headache, chills, and nausea. Where the vaccine was given the area of administration was sore and tender. Treatment information was not reported.  Company Comment: This is a Spontaneous case reported by a patient, concerning an adult male patient, with no relevant medical history, who experienced the unexpected and serious (due to medically significant) AESI of Cardiac flutter (reported as fluttering heart rate/fast heart rate), which occurred the same day after mRNA-1273.815 (SPIKEVAX 2023-2024 PFS) vaccine, administered as fourth dose within COVID-19 vaccination schedule. No information disclosed about clinical course or treatments received. The benefit-risk relationship of mRNA-1273.815 (SPIKEVAX 2023-2024 PFS) vaccine is not affected by this report.