Peer Reviewed

Peer Reviewed

Injection-Induced Axillary Nerve Injury After a Drive-Through Flu Shot

Muhammad Imran, MD1; Déon Hayley, DO2

Muhammad Imran, MD
Divisions of Allergy, Clinical Immunology and Rheumatology, Department of Internal Medicine, University of Kansas Medical Center, Kansas City, KS

Déon Hayley, DO
General and Geriatric Medicine, Department of Internal Medicine, University of Kansas Medical Center, Kansas City, KS 

Imran M, Hayley D. Injection-induced axillary nerve injury after a drive-through flu shot. Clinical Geriatrics. 2013;21(12).


Abstract: Reports of neuromuscular injuries following intramuscular influenza vaccination are rare. However, clinicians may encounter these complications with greater frequency as more adults receive the influenza vaccination. In this article, the authors present the case of an older man who reported shoulder pain and abduction weakness for 8 weeks following an intramuscular flu shot received at a drive-through clinic. He was diagnosed with injection-induced axillary nerve injury. This article briefly discusses the diagnosis and treatment of this injury and reviews techniques in line with shoulder anatomy that any healthcare professional administering the vaccine should use to minimize the risk of this injury. 

Key words: Deltoid muscle, axillary nerve, paresis, nerve damage, shoulder injections.


Millions of Americans receive influenza vaccines every year in part due to expanded community access. According to the Centers for Disease Control and Prevention (CDC), vaccination coverage tends to increase with increasing age, as older adults are considered one of the high-risk groups for flu-related hospitalization and death. During the 2011-2012 influenza season, the CDC estimated that approximately 65% of older adults aged 65 years and older in the United States received an influenza vaccine.1 Vaccination is most commonly given via intramuscular (IM) injection, with side effects of headache, muscle ache, and tiredness commonly reported. The IM injection process is considered safe, and case reports of shoulder injuries following IM injection in the United States are rare. There are reports of occasional unexpected neuromuscular complications to the axillary, radial, and sciatic nerves documented in India,2-5 Nigeria,6,7 and Korea.8 In these settings, adverse consequences after IM injections may be in part due to less rigorous training of personnel, but the greatest hazard is the pervasiveness of IM injections.

In communities across the United States, the convenience and low cost of vaccination offered through health drives, community centers, health departments, drive-through flu shot clinics, and retail pharmacies have resulted in a higher vaccination rate. More vaccinations are likely to result in more complications.9 Thus, healthcare providers should be cognizant of potential complications of vaccination.

In this article, we present a case of an older man who reported pain for approximately 8 weeks after receiving an IM influenza injection at a drive-through flu clinic. The cause of his pain was diagnosed as injection-induced traumatic axillary nerve injury. Following the case report, we review the diagnosis and treatment of this injury. For physicians, pharmacists, and nursing professionals who administer the flu vaccine in various care settings, we review administration techniques that should be used to minimize the risk of this type of injury.

Case Report

A 73-year-old right-handed man presented for evaluation of left shoulder pain and abduction weakness. He had not seen a physician for the past 15 years and he never had any regular screenings performed, but he received annual flu shots. He reported that he received a flu shot about 8 weeks earlier at a drive-through flu shot clinic offered by a hospital. He reported that directly after the injection and for weeks afterwards he experienced severe local pain at the injection site and felt like he had a “knot” in his shoulder. He never developed a rash at the injection site, but about 5 weeks after the injection, he was not able to abduct his left arm. There was no other specific trauma or other history of recent injections to his shoulder. His other extremities were unaffected and he had no neck or radicular pain or other symptoms. He also reported no preceding infectious illness, recent travels, or contact with sick people.

On physical examination, the patient pointed to the area of pain at the midpoint of his left deltoid insertion, which was slightly tender to palpation. There was notable atrophy of the left deltoid muscle, sensory loss on the lower half of the deltoid muscle, and he was unable to abduct his left arm. The patient had active range of motion of the first 10 degrees of shoulder abduction, but could not abduct beyond that. He scored a 2 on the Manual Muscle Test (MMT)10 of the deltoid, indicating poor function (25%). Passive flexion of the shoulder was normal. Flexion and extension of the forearm and rotatory movement of the shoulder were normal. Deep tendon reflexes for his bilateral biceps brachii, brachioradialis, and triceps were all normal and symmetrical (2+ grade).Other than elevated blood pressure, there were no other abnormal findings.

On the basis of the patient’s medical history, physical examination, and reported injection site, the diagnosis of injection-induced traumatic axillary nerve injury was made. The patient declined to undergo further diagnostic testing, including nerve conduction studies and magnetic resonance imaging, because he was not a Medicare beneficiary. Therefore, he was treated symptomatically with analgesics and occupational therapy, including passive and active range of motion exercises. At 1-month follow-up, his deltoid muscle showed slight improvement in contraction, sensation, atrophy, and pain. At 6 weeks after initiation of occupational therapy, the therapist reported greatly improved flexion; he was able to achieve 120 degrees of active left shoulder flexion in a seated position with a MMT score of 4-, indicating good function (75%).10


The findings of immediate pain at the time of injection, secondary isolated arm abduction weakness, and deltoid atrophy suggest our patient experienced axillary nerve injury by direct needle trauma. On the basis of his history, injection site, and physical examination and diagnostic data, we hypothesize that the likely site of injury in our patient was the anterior branch of the axillary nerve. However, injectate-related chemical neuropathy and shoulder injury related to vaccine administration (SIRVA) were also considered as possible diagnoses.

According to a search of the CDC’s Vaccine Adverse Event Reporting System (VAERS), there have been 17 reports of shoulder injury following influenza injection since 2009. Seven of these cases were in persons aged 65 years and older; two cases were diagnosed as axillary nerve damage; one case was diagnosed as brachial nerve neuritis; and one was diagnosed as complex regional pain syndrome. The other documented cases only reported pain and/or arthralgia at the injection site. The search of VAERS was conducted by Beth Hibbs, RN, MPH, Immunization Safety Office, Division of Healthcare Quality Promotion, CDC. It is important to note that VAERS is a passive reporting system, meaning that reports about adverse events can be submitted voluntarily by anyone, so data may be incorrect or incomplete. According to Ms. Hibbs, VAERS data cannot show cause and effect or be used to determine incidence or prevalence of a condition. 

In the literature, axillary and radial nerve damage has been reported as a result of deltoid IM injections given incorrectly.11 In particular, the axillary nerve and its relevant anatomy are often overlooked in deltoid IM injections. When IM injection is performed, the relation of the nerve to the site of injection should be considered. The deltoid muscle is used for nonirritating medications requiring a limited volume (0.5-1 mL). The recommended site for injection of the deltoid muscle is located two finger widths below the acromion process, with the injection performed at a 90-degree angle.12 The selection of needle size is important for obtaining appropriate depth during IM injections. In clinical practice, the standard needle length used is 16 mm (five-eighth inches), most likely because many single-dose vaccine syringes are prepackaged with five-eighth inch needles.13,14 Because needle length and injection location influence the efficacy of the administered agent, as well as adverse events (eg, intraneural, intravascular, or intrabursal injections), awareness of the relevant anatomy is of the utmost importance. 

Examining the Anatomy Around the Injection Site

The deltoid is a triangular muscle that originates from the lateral one-third of the clavicle, the superior surface of the acromion process, and the lower lip of the posterior border of the scapular spine, and it converges into the deltoid tuberosity near middle of the humerus. The axillary nerve is formedfrom the fifth and sixth cervical roots and is a terminal branch emerging from the posterior cord of the brachial plexus. The axillary nerve descends inferolaterally, anterior to the subscapularis muscle. It then passes through the quadrilateral space at theinferior border of the subscapularis muscle, where it subsequently forms medial and lateral fasciculi and ultimately anterior and posterior branches. Its anterior branch winds around the posterior surface of the surgical neck of the humerus, sending branches to the anterior and middle heads of the deltoid and a small patch of skin over its lower part. The posterior branch supplies the teres minor and the posterior aspect of the deltoid. It descends around the posterior border of the deltoid to form the upper lateral cutaneous nerve of the arm, which innervates the skin and fascia over the lower deltoid and lateral head of triceps.13,15 

Diagnosing and Treating Post-injection Injuries

Post-injection nerve damage can result from direct needle trauma, chemical irritation, toxic action of the injected solution, and neuritis (or fibrotic changes).11,16-19 When a nerve injury is caused by a needle, most patients report immediate pain at the time of injection,11 as our patient did. Neurological sequelae can range from minor transient sensory disturbances to severe sensory disturbances and paralysis.20 Diagnosis of post-injection nerve injury is usually made on a clinical basis. Most patients present with an inability to lift their arm or have paralysis of the limb after IM injection. Imaging studies, the nerve conduction velocity test, and electromyography can be administered to confirm the diagnosis and rule out other causes of nerve injury.

SIRVA is characterized by pain and limited function due to pain as opposed to paralysis, and it is caused by a localized inflammatory reaction as opposed to direct nerve damage.21 While we considered SIRVA to be a possible diagnosis in our patient, our patient presented with isolated deltoid paralysis.

Treatment for IM injection-induced injury to the nerve as well as SIRVA is mainly symptomatic, including administration of analgesics and physical therapy that may include passive and active range-of-motion exercises. 


While most adult vaccinations are administered intramuscularly in the deltoid and are generally safe, rare complications, such as nerve injury, may occur more frequently in the future as vaccinations are promoted. Practitioners should be aware of reporting systems, such as VAERS, so that ongoing standardization and quality control of vaccinations can occur. Nerve injury by IM injection is a serious and preventable complication that occurs worldwide and is likely to become more frequent in the United States with increased use of IM vaccinations. To address this potential problem, personnel who administer vaccinations should receive competency-based training and education. Alternative routes of administration may be considered to lessen risk.



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Disclosures: The authors report no relevant financial relationships.

Address correspondence to: Muhammad Imran, MD, University of Kansas Medical Center, 3901 Rainbow Blvd, MS 2026 Wescoe, Kansas City, KS 66160;