Pharmacist states that one of their technicians was administering the Spikevax PFS vaccine to a patient but while they were pushing the plunger, they were only able to administer half of the dose. They could not push any further.; Spikevax PFS vaccine to a patient but while they were pushing the plunger, they were only able to administer half of the dose, They could not push any further; No adverse event; This spontaneous case was reported by a pharmacist and describes the occurrence of UNDERDOSE (Pharmacist states that one of their technicians was administering the Spikevax PFS vaccine to a patient but while they were pushing the plunger, they were only able to administer half of the dose. They could not push any further.), DEVICE DELIVERY SYSTEM ISSUE (Spikevax PFS vaccine to a patient but while they were pushing the plunger, they were only able to administer half of the dose, They could not push any further) and NO ADVERSE EVENT (No adverse event) in a male patient of an unknown age who received mRNA-1273.815 (SPIKEVAX 2023-2024 PFS) (batch no. 3030373) for COVID-19 prophylaxis.    The suspect product included Pre-filled Syringe injection (batch no. 3030373) for COVID-19 prophylaxis.    No Medical History information was reported.   On an unknown date, the patient received fourth dose of mRNA-1273.815 (SPIKEVAX 2023-2024 PFS) (unknown route) 1 dosage form and Pre-filled Syringe (unknown route) at an unspecified dose. On an unknown date, the patient experienced UNDERDOSE (Pharmacist states that one of their technicians was administering the Spikevax PFS vaccine to a patient but while they were pushing the plunger, they were only able to administer half of the dose. They could not push any further.), DEVICE DELIVERY SYSTEM ISSUE (Spikevax PFS vaccine to a patient but while they were pushing the plunger, they were only able to administer half of the dose, They could not push any further) and NO ADVERSE EVENT (No adverse event). At the time of the report, UNDERDOSE (Pharmacist states that one of their technicians was administering the Spikevax PFS vaccine to a patient but while they were pushing the plunger, they were only able to administer half of the dose. They could not push any further.), DEVICE DELIVERY SYSTEM ISSUE (Spikevax PFS vaccine to a patient but while they were pushing the plunger, they were only able to administer half of the dose, They could not push any further) and NO ADVERSE EVENT (No adverse event) outcome was unknown.        For mRNA-1273.815 (SPIKEVAX 2023-2024 PFS) (Unknown), the reporter considered NO ADVERSE EVENT (No adverse event) to be not related. No further causality assessments were provided for UNDERDOSE (Pharmacist states that one of their technicians was administering the Spikevax PFS vaccine to a patient but while they were pushing the plunger, they were only able to administer half of the dose. They could not push any further.) and DEVICE DELIVERY SYSTEM ISSUE (Spikevax PFS vaccine to a patient but while they were pushing the plunger, they were only able to administer half of the dose, They could not push any further).  For Pre-filled Syringe, the reporter considered NO ADVERSE EVENT (No adverse event) to be not related. No further causality assessments were provided for UNDERDOSE (Pharmacist states that one of their technicians was administering the Spikevax PFS vaccine to a patient but while they were pushing the plunger, they were only able to administer half of the dose. They could not push any further.) and DEVICE DELIVERY SYSTEM ISSUE (Spikevax PFS vaccine to a patient but while they were pushing the plunger, they were only able to administer half of the dose, They could not push any further).    No concomitant medication was reported.  The pharmacist and the technician tried two more PFS (Pre-filled Syringe) but they could not completely push the plunger to get the vaccine out of the syringe. Submitting limited adverse event for the patient who was administered with the defective PFS (Pre-filled Syringe).  The Device problem code for Spikevax syringe include FDA code 1670, IMDRF code A23 which include Use of Device Problem. The Spikevax syringe device was malfunctioned and the type was CIRM  No treatment information was reported.   Most recent FOLLOW-UP information incorporated above includes: On 17-Oct-2023: Live follow received: Dose number for suspect, Patient initial, date of birth, gender has been added.