Leak occurred from the back through the plunger; Product Complaint; only received a partial dose of medication from this syringe; This non-serious case was reported by a other health professional via call center representative and described the occurrence of incomplete dose administered in a 57-year-old female patient who received Flu Seasonal QIV Dresden (Fluarix Quadrivalent 2022-2023 season) (batch number FJ4X5, expiry date 30-JUN-2024) for prophylaxis. This case was associated with a product complaint.   On 13-SEP-2023, the patient received Fluarix Quadrivalent 2022-2023 season (intramuscular, left arm). On 13-SEP-2023, an unknown time after receiving Fluarix Quadrivalent 2022-2023 season, the patient experienced incomplete dose administered (Verbatim: only received a partial dose of medication from this syringe). On an unknown date, the patient experienced syringe issue (Verbatim: Leak occurred from the back through the plunger) and pharmaceutical product complaint (Verbatim: Product Complaint).  The outcome of the incomplete dose administered, syringe issue and pharmaceutical product complaint were unknown.   This report is made by GSK without prejudice and does not imply any admission or liability for the incident or its consequences.   Additional Information: GSK Receipt Date: 13-SEP-2023 The patient experienced a leak from the back through the stopper of a Fluarix pre filled syringed.  The patient confirmed that there was no damage due to shipping.  The reporter reviewed the product information for use step by step. The patient confirmed that all operations were performed appropriately before the defect was discovered. The reporter asked at what step was the defect discovered,  the defect was discovered when the flu shot was being administered.  The suspect syringe was at the beginning of a multi pack. The reporter asked how was the mixing/shaking performed after reconstitution and or re-suspension. The reporter asked was the vial held upside down when the vaccine was being withdrawn. The product was partially administered.  There was still some product left in the syringe when the leak occurred. If health care professional preparing or administering vaccine was a new or experienced user. The HCP was an experienced user. Clearly describe which component was impacted.  The plunger was the component impacted. The reporter stated that the picture of the defect will be sent to the email address provided. The reporter reported that leaky syringe from needle connection or plunger stopper: The reporter asked where did it leak, the leak occurred from the back through the plunger stopper area. Was the syringe pre-assembled with needle some time before administration answered as no, It was less than 5 minutes between removing the syringe from the refrigerator to administration. The reporter asked what size gauge needle was used it was 25G X 0.625. The reporter asked was the blister and or carton damaged answered no. The reporter asked if leaking from plunger stopper, are there any liquid traces observed on the plunger stopper rings answered as no. The health care professional had already disposed of the product and the needle, and it was not available for return.  The reporter was a in a physician office calling to report that she was administering a dose of Fluarix to a female patient, and the medication leaked out from the back of the syringe through the plunger stopper area.  There was no accidental exposure involved in this event.  The patient only received a partial dose of medication from this syringe, which led to the incomplete dose administered.  No further information was provided about this event. The reporter consented to follow up.