lymphedema; Had blood clots in both legs down to toes/legs were swollen up; Subarachnoid hemorrhage/Was not responsive until approximately 2 weeks in; retroperitoneal bleeds; polyneuropathy; diagnosed with traumatic illness due to length of hospital stay; suffered 3 cardiac arrests; 8th day (after 2nd dose) had a neurological blackout; Felt hit by train; had underlying headache for 3-4 days then disappeared; 2nd dose arm soreness was more sore/Legs had incredible pain when he came off the ventilator from knee to hip; This spontaneous case was reported by a nurse and describes the occurrence of CARDIAC ARREST (suffered 3 cardiac arrests), LOSS OF CONSCIOUSNESS (8th day (after 2nd dose) had a neurological blackout), THROMBOSIS (Had blood clots in both legs down to toes/legs were swollen up), SUBARACHNOID HAEMORRHAGE (Subarachnoid hemorrhage/Was not responsive until approximately 2 weeks in), RETROPERITONEAL HAEMORRHAGE (retroperitoneal bleeds), POLYNEUROPATHY (polyneuropathy), CRITICAL ILLNESS (diagnosed with traumatic illness due to length of hospital stay) and LYMPHOEDEMA (lymphedema) in a male patient of an unknown age who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     No Medical History information was reported.   In December 2020, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On 25-Jan-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. In January 2021, the patient experienced VACCINATION SITE PAIN (2nd dose arm soreness was more sore/Legs had incredible pain when he came off the ventilator from knee to hip). On 02-Feb-2021, the patient experienced CARDIAC ARREST (suffered 3 cardiac arrests) (seriousness criteria hospitalization, medically significant and life threatening) and LOSS OF CONSCIOUSNESS (8th day (after 2nd dose) had a neurological blackout) (seriousness criteria hospitalization, medically significant and life threatening). On an unknown date, the patient experienced THROMBOSIS (Had blood clots in both legs down to toes/legs were swollen up) (seriousness criteria hospitalization and medically significant), SUBARACHNOID HAEMORRHAGE (Subarachnoid hemorrhage/Was not responsive until approximately 2 weeks in) (seriousness criteria hospitalization and medically significant), RETROPERITONEAL HAEMORRHAGE (retroperitoneal bleeds) (seriousness criteria hospitalization and medically significant), POLYNEUROPATHY (polyneuropathy) (seriousness criteria hospitalization and medically significant), CRITICAL ILLNESS (diagnosed with traumatic illness due to length of hospital stay) (seriousness criteria hospitalization and medically significant), LYMPHOEDEMA (lymphedema) (seriousness criterion hospitalization), FEELING ABNORMAL (Felt hit by train) and HEADACHE (had underlying headache for 3-4 days then disappeared). The patient was hospitalized for 40 days due to CARDIAC ARREST, CRITICAL ILLNESS, LOSS OF CONSCIOUSNESS, POLYNEUROPATHY, RETROPERITONEAL HAEMORRHAGE, SUBARACHNOID HAEMORRHAGE and THROMBOSIS. The patient was treated with APIXABAN (ELIQUIS) for Clot blood, at an unspecified dose and frequency; ENOXAPARIN SODIUM (LOVENOX [ENOXAPARIN SODIUM]) for Clot blood, at an unspecified dose and frequency; ACETYLSALICYLIC ACID (ASPIRINE) for Clot blood, at an unspecified dose and frequency and CLOPIDOGREL BISULFATE (PLAVIX) for Clot blood, at an unspecified dose and frequency. At the time of the report, CARDIAC ARREST (suffered 3 cardiac arrests), LOSS OF CONSCIOUSNESS (8th day (after 2nd dose) had a neurological blackout), THROMBOSIS (Had blood clots in both legs down to toes/legs were swollen up), SUBARACHNOID HAEMORRHAGE (Subarachnoid hemorrhage/Was not responsive until approximately 2 weeks in), RETROPERITONEAL HAEMORRHAGE (retroperitoneal bleeds), POLYNEUROPATHY (polyneuropathy), CRITICAL ILLNESS (diagnosed with traumatic illness due to length of hospital stay), LYMPHOEDEMA (lymphedema), FEELING ABNORMAL (Felt hit by train) and VACCINATION SITE PAIN (2nd dose arm soreness was more sore/Legs had incredible pain when he came off the ventilator from knee to hip) outcome was unknown and HEADACHE (had underlying headache for 3-4 days then disappeared) had resolved.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, Cognitive test: abnormal (abnormal) 20 out of the 40 days he was alert.     For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter did not provide any causality assessments.   Patient was naïve to medications. No concomitant medications reported. The patient was an athlete runner. The patient was very healthy before receiving the Moderna COVID-19 vaccine. The patient suffered three cardiac arrests out of the sidewalk and was put on a ventilator. He was dead out in public on sidewalk down the street. He did not had cardiac history prior. He was resuscitated 3 times in total.  Company's comment: This case concerns a male patient of unknown age with no relevant medical history, who experienced the unexpected life-threatening events of Loss of consciousness and Cardiac arrest and the unexpected serious (hospitalization) events of Subarachnoid haemorrhage, Retroperitoneal haemorrhage, Thrombosis, Critical illness, Polyneuropathy and Lymphoedema after mRNA- 1273 Moderna vaccine. The events Loss of consciousness and Cardiac arrest occurred approximately 8 days after the second dose of mRNA- 1273 vaccine and the rest of the events at a later date. Patient had sudden loss of consciousness and had 3 cardiac arrests in a public place. Cardiopulmonary resuscitation was performed and mechanical respiratory assistance was initiated. The patient was hospitalized for 40 days and required mechanical respiratory assistance for 1 week. Subarachnoid haemorrhage, Retroperitoneal haemorrhage, Thrombosis, Critical illness and Polyneuropathy were reported as complications at an unknown date. Treatment with enoxaparin, apixaban, acetylsalicylic acid and clopidogrel was given due to thrombosis at an unknown date. The rechallenge is not applicable, since the events were reported exclusively after the second dose. Treatment with enoxaparin, apixaban, acetylsalicylic acid and clopidogrel may be a confounder for Subarachnoid haemorrhage and Retroperitoneal haemorrhage, however, temporal relationship is unknown. Prolonged hospitalization may have contributed to polyneuropathy and lymphoedema. The benefit-risk relationship of mRNA- 1273 vaccine is not affected by this   This case was linked to MOD-2021-388632 (Patient Link).; Sender's Comments: This case concerns a male patient of unknown age with no relevant medical history, who experienced the unexpected life-threatening events of Loss of consciousness and Cardiac arrest and the unexpected serious (hospitalization) events of Subarachnoid haemorrhage, Retroperitoneal haemorrhage, Thrombosis, Critical illness, Polyneuropathy and Lymphoedema after mRNA- 1273 Moderna vaccine. The events Loss of consciousness and Cardiac arrest occurred approximately 8 days after the second dose of mRNA- 1273 vaccine and the rest of the events at a later date. Patient had sudden loss of consciousness and had 3 cardiac arrests in a public place. Cardiopulmonary resuscitation was performed and mechanical respiratory assistance was initiated. The patient was hospitalized for 40 days and required mechanical respiratory assistance for 1 week. Subarachnoid haemorrhage, Retroperitoneal haemorrhage, Thrombosis, Critical illness and Polyneuropathy were reported as complications at an unknown date. Treatment with enoxaparin, apixaban, acetylsalicylic acid and clopidogrel was given due to thrombosis at an unknown date. The rechallenge is not applicable, since the events were reported exclusively after the second dose. Treatment with enoxaparin, apixaban, acetylsalicylic acid and clopidogrel may be a confounder for Subarachnoid haemorrhage and Retroperitoneal haemorrhage, however, temporal relationship is unknown. Prolonged hospitalization may have contributed to polyneuropathy and lymphoedema. The benefit-risk relationship of mRNA- 1273 vaccine is not affected by this report.