Flu; Vaccination failure; Chills; Sore throat; Cough; Fever; Weakness; This is a serious spontaneous case initially received from other health professional on 28-Feb-2019, concerning a 36-year-old adult female patient.  On 02-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: right deltoid, batch number: 252664 and expiry date: 30-Jun-2019) for seasonal influenza prevention.  On 28-Feb-2019, 4 months and 26 days after vaccination, the patient experienced sore throat, cough, fever, weakness and chills and it was suspected as flu (explicitly coded as vaccination failure). It was reported that the there was no lab test performed and the patient had not taken any treatment for the events.   The patient had recovered from the event influenza (including its symptoms).   This case was associated with product quality complaint, hence quality assurance investigation (QAIR) had been requested and the corresponding QAIR reference number was 1039510. Based on the investigation performed, it was concluded that Flucelvax 252664 was manufactured in compliance with the approved internal procedures and in accordance with the quality requirements. No evidence was found that the lack of efficacy complaint was the result of the Fill Finish or Bulk manufacturing process at the facility and no trend was identified for the batch. Therefore, no internal root cause could be confirmed.   The reporter assessed the causality of the event flu as related to the suspect vaccine (reported as suspected to the suspect vaccine).   Follow up information received from other health professional on 13-Mar-2019: Reporter and patient's contact information (mailing address, email address and contact number) were added in the general tab and patient tab respectively. Patient's age was added in the patient tab. Indication of the suspect vaccination was added as seasonal influenza prevention, route of administration as intramuscular, anatomical location as right deltoid and expiry date as 30-Jun-2019 was added in the product tab. The outcome of the event cough was changed from not reported to not recovered and of the events fever, weakness and chills were changed from not reported to recovered on 04-Mar-2019 (reported as subsided after 4 days). It was reported that the there was no lab test performed and the patient had not taken any treatment for the events. Reference number: US-SEQIRUS-201902601 was added in the additional information tab. The narrative was amended accordingly.  Follow up report received from Quality assurance department on 28-Mar-2019: Based on the investigation performed, it was concluded that Flucelvax 252664 was manufactured in compliance with the approved internal procedures and in accordance with the quality requirements. The narrative was amended accordingly.  Follow-up received from other non health professional on 15-Apr-2019: Dose (0.5 ml) was added for the suspect product Flucelvax QIVc in the product tab. The patient had fully recovered from the event influenza. The outcome of the event influenza and cough was changed from 'not reported' to 'recovered'. The narrative was amended accordingly.; Reporter's Comments: A female patient of unspecified age experienced flu (manifested by sore throat, cough, fever, weakness and chills), 4 months 26 days after Flucelvax QIVc vaccination (coded to influenza and vaccination failure). Considering the fact that vaccine needs minimum 2-3 weeks to provide immune protection against influenza, vaccination failure and causal role of suspect vaccine for the event influenza cannot be ruled out and were assessed as related to suspect vaccine. The company assessed the case as serious (medically significant).