Patient was unconscious/He was unconscious for 3 minutes, without reacting; He was a bit dizzy; Pain in the arm; Patient was a little disoriented; His head was spinning; He was not feeling okay; He vanished and fell on the floor; Pain in the head; This spontaneous case was reported by a patient family member or friend and describes the occurrence of LOSS OF CONSCIOUSNESS (Patient was unconscious/He was unconscious for 3 minutes, without reacting) in an 18-year-old male patient who received mRNA-1273 (Spikevax) (batch no. 074B22A) for COVID-19 prophylaxis. The occurrence of additional non-serious events is detailed below.     Patient was a healthy and sports boy. The patient did not receive any other vaccines in the 4 weeks prior to COVID-19 vaccine.     On 16-Feb-2023, the patient received first dose of mRNA-1273 (Spikevax) (Intramuscular) 1 dosage form. On 16-Feb-2023, the patient experienced LOSS OF CONSCIOUSNESS (Patient was unconscious/He was unconscious for 3 minutes, without reacting) (seriousness criterion medically significant), DIZZINESS (He was a bit dizzy), PAIN IN EXTREMITY (Pain in the arm), DISORIENTATION (Patient was a little disoriented), VERTIGO (His head was spinning), FEELING ABNORMAL (He was not feeling okay), FALL (He vanished and fell on the floor) and HEADACHE (Pain in the head). At the time of the report, LOSS OF CONSCIOUSNESS (Patient was unconscious/He was unconscious for 3 minutes, without reacting), DIZZINESS (He was a bit dizzy), DISORIENTATION (Patient was a little disoriented), VERTIGO (His head was spinning), FEELING ABNORMAL (He was not feeling okay), FALL (He vanished and fell on the floor) and HEADACHE (Pain in the head) had resolved and PAIN IN EXTREMITY (Pain in the arm) had not resolved.        The action taken with mRNA-1273 (Spikevax) (Intramuscular) was unknown.   For mRNA-1273 (Spikevax) (Intramuscular), the reporter did not provide any causality assessments.   No concomitant medications were provided. Paramedics were taking care of the patient. They were measuring his blood pressure. The paramedics evaluated him and he was stable and bit better. But he still felt that his head was spinning. The patient went to the urgent care and received an IV solution, and he was feeling better, stable, didn´t feel dizzy so patient went home. Since then patient stated that his arm hurted.The caller stated that his son was okay now, he was not feeling bad nor dizzy.  Company comment: This spontaneous case concerns a 18-year-old male patient with no medical history reported, who experienced serious (medically significant) unexpected event of loss of consciousness which according to witnesses, occurred instantly after receiving a dose of mRNA-1273, which was the patient's 1st dose of COVID-19 vaccination schedule. Paramedics arrived and assisted with checking vital parameters. The patient regained consciousness after app. 3 minutes; was a little disoriented; reported also vertigo, headache, arm pain, dizziness and feeling abnormal. The patient was taken to emergency room where he has felt better after intravenous solution so was discharged home. The patient age and higher risk of vasovagal reflex in young patients population could be considered a risk factor to the event.  No further details on clinical course and any diagnostic work up were provided for review. The event was resolved at the time of report. The benefit-risk relationship of mRNA-1273 is not affected by this report.  Event seriousness was assessed as per Reporter.   This case was linked to US-MODERNATX, INC.-MOD-2023-714122, US-MODERNATX, INC.-MOD-2023-714200 (Linked Report).; Sender's Comments:  US-MODERNATX, INC.-MOD-2023-714122:Mother-In-Law US-MODERNATX, INC.-MOD-2023-714200:Reporter