Swelling on both legs; Rash [and swelling] on her both legs; Joint pain (on her knuckles, on hands); C reactive protein was elevated to 90; Panic; Dehydrated; Not feeling well; Fatigue; Headache; Fever at night (low grade 100F)/fever escalated to 102-103F/fever (about 101F)/Fever got up to 104F; This is a serious spontaneous case, initially received from other non-health professional on 26-Nov-2018, concerning a 43-year-old, adult, female patient.   The patient's current condition included hypothyroidism (reported as medical history) and concomitant medication included Synthroid (levothyroxine sodium).   On 10-Oct-2018, the patient was administered Flucelvax QIVc [influenza vaccine, subunit influenza virus vaccine polyvalent, cell-culture-derived; dose: 0.5 ml, route of administration: intramuscular, anatomical location: deltoid, batch number: 252667, expiry date: 30-Jun-2019] for influenza prophylaxis. It was reported that it was the first year the patient received an egg free vaccine, although she was not allergic to egg.   On 11-Oct-2018, 1 day after vaccination (reported as in the evening), the patient was not feeling well. The patient reported headache and fatigue initially, which progressed to fever at night (reported as low-grade fever with 100 F). The patient took ibuprofen, and fever resolved initially, but fever would go up again without ibuprofen.   On 13-Oct-2018 (Saturday) and 14-Oct-2018 (Sunday), fever escalated to 102 to 103 F.   On 15-Oct-2018 (Monday), the patient went to urgent care and the patient was told that the she must have contracted a virus and should be better in a few days. The patient continued ibuprofen for fever as per the advice.    On 17-Oct-2018 (Wednesday), the patient was told that she should feel better in the urgent care, the headache and fever (about 101 F) wouldn't subside unless there was medication. Later, on the same day, the fever elevated up to 104 F. The patient experienced rash and swelling on her both legs accompanied with joint pain (on her knuckles and hands). At that point of time, the patient started to panic and went to urgent care again. The patient was dehydrated and unspecified lab tests were performed (results were not provided). C-reactive protein was elevated to 90 (units and normal range was not provided). The patient was initially hydrated and was treated with IV antibiotic therapy (the reporter was not sure of cefazolin or ceftriaxone) along with Solu-medrol (Methylprednisolone sodium succinate) that same night. The patient was also tested for flu, but the results were negative with no other symptoms. The patient was discharged from the urgent care eventually.   On 18-Oct-2018, the patient visited the urgent care for follow-up. At that point, the rash was fading down, but fever lingered. The previous lab tests were performed again which revealed decreasing C-reactive protein values. Viral and bacterial infections were ruled out along with immune system disorders. It was reported that the health personnel could not figure out what was going on. On 21-Oct-2018 (for about 10 days), it was reported that fever continued to persist.   On 25-Oct-2018 (within 14 days), the symptoms resolved, and the patient was completely normal.; Reporter's Comments: A 43-year-old female patient was feeling unwell and experienced headache, fatigue and fever, 1 day after vaccination along with rash on both legs, swelling of legs, joint pain, panic reaction, dehydration and C-reactive protein increased, 7 days after vaccination with suspect vaccine Flucelvax QIVc.The company assessed the causality of the events dehydration, malaise, swelling of legs, fatigue, headache, fever, rash on both legs and joint pain as related considering the plausible temporal relationship between events and suspect vaccine and not related for the events C-reactive protein increased and panic reaction considering C-reactive protein increased as a laboratory finding and panic reaction can be explained alternatively by the reported events.