Vaccination failure; Diagnosed with flu (Strain A); Fever; Chills; Body aches; Headache; Congestion; Cough; Flu (Strain A); This is a spontaneous case, initially received from other non-health professional on 21-Feb-2019, concerning a 64-year-old, adult male patient.  The patient had no medical history. The patient had not received any concomitant medications.  On 11-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 21-Feb-2019, 4 months and 10 days after vaccination, the patient experienced fever, chills, body aches, headache, congestion and cough.  On 22-Feb-2019, the patient started his treatment with Tamiflu (oseltamivir phosphate) for the event and took for 5 days.   On 23-Feb-2019, the patient was diagnosed with strain A flu (influenza A virus test positive) (explicitly coded as vaccination failure).  It was reported that, the patient was not hospitalized.  The symptoms of flu was recovered on 24-Feb-2019. The patient was back to his work and felt much better.  This case was associated with product quality complaint, hence quality assurance investigation (QAI) 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 determined.  The reporter assessed the case as serious (medically significant).  Follow up report received from the other health professional on 07-Mar-2019: Reporter's institution was added in the general tab. Start date of the treatment medication was updated (22-Feb-2019) and the duration of treatment was 5 days. New symptoms (fever, chills, body aches, headache, congestion and cough) were added in the event tab and were mapped to the diagnosis influenza A virus infection. The stop date of the event influenza A virus infection was updated to 24-Feb-2019 from 26-Feb-2019. The Med info number (SEQ19-01005) was added in the additional information tab. The narrative was amended accordingly.  Follow up report received from the other non-health professional on 07-Mar-2019: The reporter confirmed that all the symptoms fever, chills, body aches, headache, congestion and cough were recovered on 24-Feb-2019 (added stop dates in the event tab). The med info number (SEQ19-01043) was added in the additional information. QAIR reference number: 1039510 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.; Reporter's Comments: A 64-year-old male patient experienced unspecified symptoms of flu and was diagnosed with strain A flu, 4 months 10 days after Flucelvax QIV 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.