Fatigue; Joint and muscle pain; Joint and muscle pain; Hives; Headache; Edema; This spontaneous case was received on 29-Jun-2022 from other non-healthcare professional (consumer's mother) via Agency (reference number: SEQW22-01682) and concerned a 13-year-old, female patient.  The patient had no medical history and was not taking any concomitant medications (had Albuterol (salbutamol) prescribed at the time but it was not used). The patient had no allergies. The patient was very healthy and active.  On 17-Oct-2020, the patient was vaccinated with Flucelvax Quadrivalent (prefilled syringe (PFS)) (influenza vaccine inact sag 4v; dose: 0.5 ml, route of administration and anatomical location: not reported) for influenza prophylaxis. The batch number reported was 279844 and expiry date was 30-Jun-2021.   On an unspecified date in Oct-2020, within three or four days after receiving Flucelvax Quadrivalent the patient developed fatigue and joint pain.    On an unspecified date in 2020, an unknown amount of time after receiving Flucelvax Quadrivalent, the patient experienced hives, joint and muscle pain increased, and she developed edema. Also, the patient experienced headache. The patient was treated with unspecified antihistamines and unspecified over the counter medications which did not help.  On 01-Dec-2021, the patient was hospitalised.   On an unspecified date in Dec-2020, the patient was treated with intravenous (IV) prednisone.   On 06-Dec-2021, the patient was discharged from hospital.   On an unspecified date, the patient had tried unspecified immunosuppressive medications and tons of unspecified antihistamines and nothing worked. The patient had done extensive blood work, but the results were not reported.   At the time of initial reporting, the patient had not recovered from the events of hives, muscle pain, joint pain, fatigue and headache. She had subsequent prednisone prescribed over the past 20 months and nothing worked, as reported.  The outcome of the event of edema was not reported.  The reporter assessed the events as related to Flucelvax Quadrivalent. The patient's mother wanted to identify what patient's body could still be reacting to from this vaccine.   All events were considered as serious due to the seriousness criterion of hospitalization.  Company comment: A 15-year-old patient developed fatigue and arthralgia reportedly within three or four days after receiving the suspect product Flucelvax Quadrivalent. The patient also experienced urticaria, myalgia, oedema, and headache an unknown amount of time after vaccination. Based on plausible temporal relationship, causality for the events fatigue and arthralgia is assessed as possibly related. For the rest of the events causality is unassessable, due to lack of information and unclear temporal relationship.; Reporter's Comments: The patient's mother wanted to identify what patient's body could still be reacting to from this vaccine.; Sender's Comments: A 15-year-old patient developed fatigue and arthralgia reportedly within three or four days after receiving the suspect product Flucelvax Quadrivalent. The patient also experienced urticaria, myalgia, oedema, and headache an unknown amount of time after vaccination. Based on plausible temporal relationship, causality for the events fatigue and arthralgia is assessed as possibly related. For the rest of the events causality is unassessable, due to lack of information and unclear temporal relationship.