This spontaneous case was reported by a patient and describes the occurrence of LOSS OF CONSCIOUSNESS (knocked her out) in a 57-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 058E21A and 056M21) for COVID-19 prophylaxis. The occurrence of additional non-serious events is detailed below. Previously administered products included for COVID-19 vaccination: Pfizer (Batch no- EN6208 intramuscularly) on 22-Mar-2021 and Pfizer (Batch no- EW0153) on 12-Apr-2021; for Product used for unknown indication: Flu vaccine in October 2021. Past adverse reactions to the above products included No adverse event with Flu vaccine, Pfizer and Pfizer. Concurrent medical conditions included Allergy to antibiotic, Drug allergy (codeine) and Overweight. On 05-Sep-2021, the patient received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) .5 milliliter. On 23-Jun-2022, received fourth dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) dosage was changed to .25 milliliter. On 05-Sep-2021, the patient experienced LOSS OF CONSCIOUSNESS (knocked her out) (seriousness criterion medically significant), OVERDOSE (1st Moderna booster dose was full dose), PARAESTHESIA (tingly lips, tip of tongue felt tingly/ tingly face on the left side), PYREXIA (fever) and CHILLS (chills). On an unknown date, the patient experienced INTERCHANGE OF VACCINE PRODUCTS (Interchange of vaccine products). At the time of the report, LOSS OF CONSCIOUSNESS (knocked her out), PARAESTHESIA (tingly lips, tip of tongue felt tingly/ tingly face on the left side), PYREXIA (fever) and CHILLS (chills) had resolved and OVERDOSE (1st Moderna booster dose was full dose) and INTERCHANGE OF VACCINE PRODUCTS (Interchange of vaccine products) outcome was unknown. It was unknown if patient had been diagnosed with or tested positive for COVID-19. No concomitant medication was reported by patient. No treatment medication was reported by patient. Company comment- This spontaneous case concerns a female patient aged 57 years, with no relevant medical history reported, who experienced the unexpected serious (medically significant) event of Loss of consciousness after 1st booster dose of mRNA-1273 vaccine. The event occurred on the same day along with non serious events of Paraesthesia, Overdose (1st Moderna booster dose was full dose), Pyrexia and Chills. Interchange of vaccine products was noted as patient had received initial schedule of vaccination with TOZINAMERAN. Clinical course, lab reports and treatment details were not reported. The outcome of events was resolved at the time of report. The benefit-risk relationship of mRNA-1273 is not affected by this report. Events seriousness was assessed based on medical judgement. This case was linked to MOD-2022-594941 (Patient Link). Sender's Comments: This spontaneous case concerns a female patient aged 57 years, with no relevant medical history reported, who experienced the unexpected serious (medically significant) event of Loss of consciousness after 1st booster dose of mRNA-1273 vaccine. The event occurred on the same day along with non serious events of Paraesthesia, Overdose (1st Moderna booster dose was full dose), Pyrexia and Chills. Interchange of vaccine products was noted as patient had received initial schedule of vaccination with TOZINAMERAN. Clinical course, lab reports and treatment details were not reported. The outcome of events was resolved at the time of report. The benefit-risk relationship of mRNA-1273 is not affected by this report. Events seriousness was assessed based on medical judgement.