Chronic fatigue syndrome; Fibromyalgia; Whole body became inflamed; Stomachache; Difficult to walk; Difficulty breathing; Very fatigued; Headache; Muscle and joint pain; Muscle and joint pain; This spontaneous was received on 03-Mar-2021 from other non-health professional (consumer) via (reference number: SEQW21-00892) with additional information received on 11-Mar-2021 (reference number: SEQW21-00967) (being processed together) and concerned a 50-year-old, female patient.  The patient had no relevant medical history. The patient's concomitant medications were not reported.   On 29-Jan-2020, the patient was vaccinated with Flucelvax Quadrivalent (influenza vaccine, subunit influenza virus vaccine polyvalent; dose: 0.5 mL, route of administration: intramuscular and anatomical location: left deltoid) for protection against seasonal influenza. The batch number reported was 261229 and expiry date was 30-Jun-2020.  On an unspecified date in Jan-2020, approximately 48 hours after receiving Flucelvax Quadrivalent, the patient's whole body became inflamed. The patient became very fatigued and developed a stomachache, severe headache, muscle and joint pain that made her walking difficult. The patient stated that she also had difficulty breathing around that time, but that did not last long. It was also reported that they were not sure if the patient had chronic fatigue syndrome and fibromyalgia before and it exacerbated after receiving the vaccine or if she developed these issues after receiving the vaccine. The patient was seeing an allergist to figure out what was going on.  On an unspecified date, the patient recovered from the event of difficulty breathing.  At the time of initial reporting on 03-Mar-2021, the patient had not recovered from the events of 'walking difficulty', 'fatigue', 'muscle pain' and 'joint pain'. The patient stated that she was still experiencing some of these issues to date and "still had stuff going on in her body".  The outcome of the events of 'inflammation', 'stomachache' and headache was not reported.   The reporter did not provide a causality assessment.  The reporter assessed the case as non-serious.  Company comment: A 50-year-old patient was vaccinated with Flucelvax Quadrivalent. Approximately 48 hours after receiving Flucelvax Quadrivalent, the patient's whole body became inflamed. The patient became very fatigued and developed stomach ache, severe headache, muscle and joint pain that made her walking difficult. The patient stated that she also had difficulty breathing around that time, but that did not last long. It was also reported that they were not sure if the patient had chronic fatigue syndrome and fibromyalgia before and it exacerbated after receiving the vaccine or if she developed these issues after receiving the vaccine. Due to unclear information regarding inflammation, chronic fatigue syndrome and fibromyalgia, causality is unassessable for these events. More information regarding diagnostic findings is needed. The events of headache, abdominal pain upper, gait disturbance, dyspnoea, myalgia and arthralgia are assessed as possibly related, due to plausible chronology.; Sender's Comments: A 50-year-old patient was vaccinated with Flucelvax Quadrivalent. Approximately 48 hours after receiving Flucelvax Quadrivalent, the patient's whole body became inflamed. The patient became very fatigued and developed stomach ache, severe headache, muscle and joint pain that made her walking difficult. The patient stated that she also had difficulty breathing around that time, but that did not last long. It was also reported that they were not sure if the patient had chronic fatigue syndrome and fibromyalgia before and it exacerbated after receiving the vaccine or if she developed these issues after receiving the vaccine. Due to unclear information regarding inflammation, chronic fatigue syndrome and fibromyalgia, causality is unassessable for these events. More information regarding diagnostic findings is needed. The events of headache, abdominal pain upper, gait disturbance, dyspnoea, myalgia and arthralgia are assessed as possibly related, due to plausible chronology.