Between the syringe (barrel) and the luer lock was leaked/Is the luer lock damaged Yes. The luer lock was loose and spinning/ her colleague overtightened the needle and perhaps this caused a crack; Between the syringe (barrel) and the luer lock was leaked/Is the luer lock damaged Yes. The luer lock was loose and spinning/ her colleague overtightened the needle and perhaps this caused a crack; While administering Bexsero the syringe leaked and an incomplete dose of unknow volume was administered to a patient; 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 16-year-old male patient who received Men B NVS (Bexsero) (batch number 4L274, expiry date 30-SEP-2024) for prophylaxis. This case was associated with a product complaint.  On 31-MAY-2023, the patient received Bexsero. On 31-MAY-2023, an unknown time after receiving Bexsero, the patient experienced incomplete dose administered (Verbatim: While administering Bexsero the syringe leaked and an incomplete dose of unknow volume was administered to a patient). On an unknown date, the patient experienced syringe issue (Verbatim: Between the syringe (barrel) and the luer lock was leaked/Is the luer lock damaged Yes. The luer lock was loose and spinning/ her colleague overtightened the needle and perhaps this caused a crack) and pharmaceutical product complaint (Verbatim: Between the syringe (barrel) and the luer lock was leaked/Is the luer lock damaged Yes. The luer lock was loose and spinning/ her colleague overtightened the needle and perhaps this caused a crack). 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: 31-MAY-2023 and 01-JUN-2023 The Healthcare Professional (HCP) who was preparing the dose an experienced user. The suspected syringe (with the needle attached) had been put in sharps container. All other syringes in the suspect box look fine and their luer lock tips were secure. The suspected syringe luer lock was loose and spinning. Credit 1/10 box (one dose) to vaccines for children account. During the administration step, the defect was discovered. Between the syringe (barrel) and the luer, lock device (NOT between needle and luer lock). The syringe was not pre-assembled with needle some time before administration. The 25 into 1-inch gauge size was used for administration. The blister and/or carton was not damaged. The leaking from plunger stopper and it was not applicable if there were any liquid traces on the plunger stopper rings was observed. The luer lock was damaged. The luer lock was loose and spinning. The Medical Assistant (MA) who was the reporter was not the one who had prepared/administered the suspect product but her theory was that perhaps the person who attached the needle might have turned it too tight.  She thought maybe her colleague had overtightened the needle and perhaps this had caused a crack.  The reporter stated that, they had taken the needle out of package, taken the rubber tip off the luer lock, then they put the needle on the lure lock and turn it about a quarter of inch until secured. The needle, which was used, was not available. There was no damage/breakage on the syringe barrel was observed. The vaccine administration facility was the same as primary reporter. The reporter consented to follow up. While administering Bexsero the syringe leaked and an incomplete dose of unknown volume was administered to a patient, which had led to incomplete dose administered.