Flu vaccination is rarely associated with subdeltoid bursitis, study finds
Clinicians could benefit from an injection technique “tune-up” in needle placement and needle length, an editorial suggested.
Although there was an increased risk for subdeltoid bursitis in the deltoid muscle after intramuscular influenza vaccination, the absolute risk was small, a study found.
To estimate the risk for subdeltoid bursitis after flu vaccination, researchers conducted a retrospective cohort study based on data from The Vaccine Safety Datalink on nearly 3 million persons who received an inactivated influenza vaccine during the 2016-2017 flu season. Researchers used a self-controlled risk interval analysis to calculate the incidence rate ratio of bursitis in a risk interval of 0 to 2 days after vaccination versus a control interval of 30 to 60 days. Attributable risk was also estimated. The study was funded by the CDC and results were published June 23 by Annals of Internal Medicine.
There were 1,098 presumptive cases of bursitis. The researchers applied random sampling to select 526 presumptive cases for medical record abstraction, of which 421 met the case definition for an incident diagnosis of subdeltoid bursitis. Symptoms began after vaccination for 257 cases. Sixteen (6.2%) had symptom onset in the risk interval, 51 (19.8%) had symptom onset in the control interval, and 190 (74.0%) had symptom onset in neither interval. The median follow-up after vaccination for cases was 576 days (range, 189 to 781 days).
The median age of affected patients was 57.5 years (range, 24 to 98 years), and 69% were women. The self-controlled risk interval analysis found an increased risk for subdeltoid bursitis with symptom onset within three days of vaccination compared with the 30 to 60 days afterward (incidence rate ratio, 3.24; 95% CI, 1.85 to 5.68). This corresponds to an attributable risk of 7.78 (95% CI, 2.19 to 13.38) excess cases of subdeltoid bursitis during the three days after vaccination per 1 million persons vaccinated, the researchers calculated.
Among definite cases in the risk interval, four had surgical procedures for bursitis or mentioned bursitis on surgical reports. The intervals from vaccination to surgery were 90, 115, 210, and 266 days. Four definite cases had findings of bursitis on magnetic resonance imaging at 11, 101, 167, and 217 days after vaccination. One definite case reported a positive effect of a corticosteroid injection in the affected shoulder. The one probable case was diagnosed with bursitis by an orthopedic surgeon.
Resolution of symptoms was documented in the medical record for two of the 16 (12.5%) risk interval cases (by 62 and 207 days after symptom onset). A similar proportion of control interval cases (five of 51 [9.8%]) had symptom resolution documented. The 14 risk interval cases without documented resolution of symptoms had a median time to the last visit with persistent shoulder symptoms of 386 days (range, 21 to 781 days), whereas the median for control interval cases was 95 days (range, 4 to 690 days).
The authors wrote that risks for adverse events such as subdeltoid bursitis must be weighed against the benefits of vaccination, noting that for the studied year, the CDC estimated that flu vaccination prevented more than 5.2 million illnesses, 2.6 million medical encounters, 72,000 hospitalizations, and 5,000 deaths.
An accompanying editorial said that administration technique may play a role in shoulder injury, and clinicians could all benefit from an injection technique “tune-up” in needle placement and needle length. Those giving vaccines should know anatomical landmarks to aim for the midpoint of the deltoid muscle, two to three fingers' width below the acromion process (and above the armpit). Clinicians should inject at a 90° angle, and no aspiration is needed, the editorial said. Correct needle length depends on weight and sex, and the object is to inject into the muscle, not through it, which can put the bursa at risk, it noted.
“The ongoing coronavirus disease 2019 pandemic may present challenges during the upcoming flu season for traditional practice models that may otherwise have relied on the in-office flu clinic to ensure patients get vaccinated,” the editorial concluded. “[W]ith the prospect of more drive-thru clinics, an increasing urgency to vaccinate, and the possibility of needing to administer several vaccines—sometimes in nontraditional settings—it is now more important than ever to insist that patients be sure to dress appropriately (either sleeveless or with loose sleeves) to facilitate efficient and safe vaccine administration. Unbuttoning the first 2 buttons of a long sleeve shirt—or the second and third buttons so you can keep your tie on— will not work.”