Vaccination failure; Diagnostic test (nasal swab test) was performed with positive result for the flu; Fever; Body aches; Malaise; Fatigue; Flu; This is a spontaneous case, initial and follow up received from other health professional (nurse) on 19-Feb-2019 (both the versions being processed together), concerning a 52-year-old, adult male patient.  The patient's historical vaccine included influenza vaccine (for several years) with no adverse event. The patient's current condition included high blood pressure. The concomitant medication included an unspecified high blood pressure medication.  On 18-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: 252664 and expiry date: 30-Jun-2019) for active immunization against influenza.  On 12-Feb-2019, 3 months and 25 days after vaccination, the patient experienced fever, body aches, malaise and fatigue. On 15-Feb-2019, nasal swab test was performed, and the result was positive for flu, but the specific strain of virus was unknown (considered as vaccination failure).  The patient had recovered from the event influenza, malaise and fatigue on 22-Feb-2019 while the events pain and fever resolved on 19-Feb-2019.  Quality Assurance Investigation of batch number 252664 was noted (QAI reference number: 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 case as serious (medically significant).  Non-significant follow up received from the quality assurance team (QA) on 05-Mar-2019: The Quality Assurance Investigation of batch number 252664 was added (QAI reference number: 1039510) in additional information tab. The narrative was amended accordingly.  Follow-up received from the reporter on 05-Mar-2019: Institution and email address of the secondary reporter was added in the general information tab. Added current condition (blood pressure high) and historical vaccine (influenza vaccine with no adverse event) were added in the patient tab. Lab data swab test (influenza virus test) was added in the patient tab. Added new events fatigue' and influenza virus test positive' were added in the event tab. Start date of the events: influenza, fever, pain and malaise was changed from '15-Feb-2019' to '12-Feb-2019' in the event tab. Stop date 22-Feb-2019 was added for the events: influenza, malaise and fatigue. The events pain and fever resolved on 19-Feb-2019 was added in the event tab. The outcome of the events influenza, fever, pain and malaise was changed from unknown to recovered. The narrative was amended accordingly.  Follow up received from the Quality assurance department on 28-Mar-2019: The QA investigation report was updated. The narrative was amended accordingly.; Reporter's Comments: A 52-year-old male patient experienced influenza (fever, bodyache, malaise, fatique and vaccination failure), 3 months and 25 days post-vaccination with Flucelvax QIVc. 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. Further assessment will be done upon receipt of new information.