A 22-year-old woman with no significant medical history developed acute left shoulder pain and severe restrictions in range of motion after a seasonal influenza vaccine injection. Imaging by MRI, approximately 8 weeks after the injection, and by ultrasound, approximately 9.5 weeks after the injection demonstrated contusions on the humerus, injury of the supraspinatus, and effusion in the subacromial bursa. Her reaction was reported to the Vaccine Adverse Event Reporting System as a case of shoulder injury related to vaccine administration, likely due to injection of the influenza vaccine into the subacromial bursa. This case serves as a catalyst for discussion regarding vaccination technique and the potential to prevent complications arising from vaccine overpenetration.