Cardiac arrest; Brain damage; Passed away; This spontaneous case was received on 03-Oct-2021 from other non-health professional (consumer's daughter) via Med Communications (reference number: SEQW21-03202) and concerned a 75-year-old, male patient.  The patient's concurrent conditions included low B vitamin levels. The patient's concomitant medications included levothyroxine and Flomax (tamsulosin hydrochloride), both used for an unreported indication. It was reported that the patient was healthy and active and had not experienced any anaphylaxis or adverse events previously. Also, the patient was tested negative for COVID 19. It was reported that the patient completed full physical, electrocardiogram (EKG) and lab work prior vaccination and received a ''clean bill of health''.  On 25-Sep-2020, the patient was vaccinated with Flucelvax Quadrivalent (influenza vaccine, subunit influenza virus vaccine polyvalent; dose, route of administration: intramuscular, anatomical location: deltoid and indication: not reported) as a prevention of seasonal influenza. The batch number reported was 283847 and expiry date 30-Jun-2021.   On 30-Sep-2020, five days after receiving Flucelvax Quadrivalent, the patient suffered a cardiac arrest at home and was not revived for an extended length of time. He was rescued in the emergency room (ER) and was admitted to hospital, in the intensive care unit (ICU). The patient was subjected to several resuscitation attempts and received several epinephrine injections. He was in a hospital for two weeks and maintained on life support and ventilators. However, treating physicians and neurologist determined after several magnetic resonance imaging (MRIs) the patient had gone too long without oxygen and suffered from brain damage.  On an unspecified date in Oct-2020, reported as five days after cardiac arrest (discrepant information since it was reported that the patient was hospitalized for two weeks), the patient passed away. The cause of death was not reported. It was not reported if autopsy was performed.  The outcome of brain damage and cardiac arrest was not reported.   The reporter assessed all events as related to Flucelvax Quadrivalent. The reporter strongly suspected that her healthy and active father had an adverse reaction to Seqirus flu shot.   The reporter assessed events of brain damage and cardiac arrest as serious due to hospitalisation and additionally, all events of were considered to be medically significant by a Physician within Seqirus' Pharmacovigilance and Risk Management Department.  Company comment: A 75-year-old, male patient was vaccinated with the suspect product Flucelvax Quadrivalent. Five days after vaccination the patient experienced a cardiac arrest. As reported the patient was too long without oxygen and suffered from brain damage. Brain damage was confirmed after several magnetic resonance imaging (MRIs). Causality for this event is assessed as not related to suspect product based on described alternative aetiology. The patient died after five days (discrepant information). Cause of death and autopsy report have not been provided. Due to limited information causality for the event death is unassessable. Although chronology is plausible, lack of information regarding diagnostic findings preclude proper causality assessment of the reported cardiac arrest. Therefore, causality for this event is unassessable.; Reporter's Comments: The reporter strongly suspected that her health and active father had an adverse reaction to Seqirus flu shot.; Sender's Comments: A 75-year-old, male patient was vaccinated with the suspect product Flucelvax Quadrivalent. Five days after vaccination the patient experienced a cardiac arrest. As reported the patient was too long without oxygen and suffered from brain damage. Brain damage was confirmed after several magnetic resonance imaging (MRIs). Causality for this event is assessed as not related to suspect product based on described alternative aetiology. The patient died after five days (discrepant information). Cause of death and autopsy report have not been provided. Due to limited information causality for the event death is unassessable. Although chronology is plausible, lack of information regarding diagnostic findings preclude proper causality assessment of the reported cardiac arrest. Therefore, causality for this event is unassessable.; Reported Cause(s) of Death: Unknown cause of death