strained muscle of rotator cuff; Shoulder pain; restricted range of motion following injection of IIV into the upper arm; This case was reported in a literature article and described the occurrence of rotator cuff injury in a elderly patient who received Flu unspecified (Flu vaccine) for prophylaxis.   On an unknown date, the patient received Flu vaccine. On an unknown date, less than a week after receiving Flu vaccine, the patient experienced rotator cuff injury (serious criteria hospitalization and other: as per reporter), injected limb mobility decreased (serious criteria hospitalization and other: as per reporter) and shoulder pain (serious criteria hospitalization and other: as per reporter). On an unknown date, the outcome of the rotator cuff injury, injected limb mobility decreased and shoulder pain were unknown.   The reporter considered the rotator cuff injury, injected limb mobility decreased and shoulder pain to be related to Flu vaccine.  Additional details were reported as follows: This case was reported in a literature article and described the occurrence of shoulder pain with strained muscle of rotator cuff patient aged between 24 and 92 years of unspecified gender, who was vaccinated with unspecified inactivated seasonal influenza vaccine (IIV) (manufacturer unknown) for prophylaxis. The patient was a part of descriptive analysis that aimed to describe case reports of atypical shoulder pain and dysfunction following injection of inactivated influenza vaccine (IIV). The data searched from the vaccine Adverse Event Reporting System (VAERS) database from July 2010 to June 2017 for reports of atypical shoulder pain and dysfunction following IIV. [In this study, the classified reports into three categories: confirmed (i.e., met the criteria of our case definition), indeterminate, or not a case. Reports that met the regulatory definition for serious were independently reviewed by the physician. Excluded reports that described symptoms lasting less than 7 days and those in which the report date was less than 7 days following vaccination]. The patient had no brachial neuritis. The patient had not received more than one vaccine was administered in the arm of the affected shoulder (multiple vaccinations not given simultaneously) and the patient had no prior history of chronic pain, inflammation, or injury with recurrent symptoms in the affected shoulder. The patient was from confirmed serious case category. No information on patient's family history or concomitant medication was provided. On an unspecified date, the patient received unspecified inactivated influenza vaccine (IIV) in the upper arm (administration route unspecified; dosage unknown; batch number not provided). The age of vaccination was not provided. On an unspecified date between 1st July 2010 and 30th June 2017 (2010-2011 through 2016-2017 influenza seasons), less than 48 hours after vaccination, the patient had experienced shoulder pain with strained muscle of rotator cuff and was hospitalized. [In this study, case definition or criteria included shoulder pain and restricted range of motion following injection of IIV into the upper arm with symptom onset less than 48 h after IIV vaccination and a duration of greater than seven days (to differentiate from injection site reactions). The patient discharged. This case has been considered serious due to hospitalization and as per author. [In this study, for the purpose of IIV vaccination among the 90 cases that met the regulatory definition of serious as specified in Regulations defined as a report was classified as serious if any of the following were described death, life-threatening illness, hospitalization or prolongation of existing hospitalization, permanent disability, congenital anomaly or birth defect, or intervention to prevent the aforementioned outcomes].  Treatment was unknown. [In this study, eight of the 11 hospitalized cases described patients who underwent surgery of the affected shoulder joint. Treatments prescribed in 546 reports, of those 254 non-narcotic analgesics; 215 physical therapy; 109 corticosteroid injection; 89 hot and cold therapy; 79 oral steroids; 28 narcotic analgesics; 19 home shoulder exercise; 17 pain medication; not specified; 16 surgery; 15 muscle relaxants;10 topical analgesics; 10 massage; 7 chiropractic; 6 sling; 4 acupuncture; 2 shoulder manipulation under sedation; 2 antibiotics; 2 muscle stimulators; other includes: rest, restrictions for arm, shoulder taped, anticonvulsants, iontophoresis, sedatives, fluids, yoga, mud patches, and treatment not specified]. The outcome of the events were not reported. [In the study, in 1057 reports, signs and symptoms had not resolved at the time a report was made to VAERS]. In 50 reports, symptoms had resolved at time of report; median duration to recovery was 70 days (range 18-365 days). The remaining 113 reports did not state whether the symptoms had resolved.]. The authors commented, "This was the first large-scale, post-licensure vaccine safety review of atypical shoulder pain and dysfunction following influenza vaccination. Our results suggest that reports of atypical shoulder pain and dysfunction following IIV were uncommon, given the amount of influenza vaccine distributed." we cannot conclude that these reports represent true incident shoulder injuries caused by vaccination. However, we also cannot rule out that some of these cases might be new shoulder injuries or aggravation of existing shoulder injuries resulting from improperly administered vaccines too close to the underlying structures and tissues of the shoulder joint. Reasons for the increase in shoulder injury related to vaccine administration (SIRVA) claims filed with the Compensation Program (CP) were likely due to factors other than a true increase in causally-associated vaccine-related shoulder injuries. The CP covers all vaccines routinely recommended for use in children regardless of the age of the vaccine recipient. While we cannot establish cause and effect based on VAERS reports, these findings suggest that improper placement of an intramuscular vaccine injection too high on the arm and too close to the underlying structures of the shoulder joint might be a possible contributing factor for atypical shoulder pain and dysfunction. It is possible that some individuals in our analysis had minor shoulder problems unrelated to vaccination that would subsequently resolve; however, in most reports, we were unable to determine how long the shoulder pain and dysfunction persisted because reports were made to VAERS while patients were still experiencing signs and symptoms. Reported contributing factors, such as IIV given too high" on the arm are primarily subjective, self-reported, and not verifiable. In most reports, documentation of past medical history was limited so pre-existing shoulder problems or other risk factors that could explain signs and symptoms might not have been identified. However, based on VAERS reports alone, we cannot draw any conclusions about a potential association with respect to place of vaccination. The author concluded, "Reports to VAERS of atypical shoulder pain and dysfunction following IIV were relatively uncommon and stable during the seven influenza seasons in our review, with no indication of a recent increase in reporting. In total, we identified 1220 reports during a time period in which almost 1 billion doses of IIV had been distributed. Some of these case reports might represent true shoulder injuries that were caused or aggravated by an improperly administered vaccine. If some of these reports are the result of poor injection technique then they are preventable. Healthcare provider awareness, education and training, and adherence to best practices for vaccine administration are important focus areas for prevention. CDC has resources available on safe vaccine administration practices. Efforts to address healthcare practice issues around potential shoulder injuries related to vaccination could include the development of a standardized case definition similar to what has been done with local injection site reactions, evaluation of pathophysiology and risk factors, and determining best injection practices and effective prevention and treatment options." This is 1 of the 6 valid cases reported in this literature article.