Investigators identified an increased risk for subdeltoid bursitis following administration of the influenza vaccine; however, the absolute risk was found to be small, according to study results published in the Annals of Internal Medicine.1
Subdeltoid bursitis has been reported to be an adverse event associated with intramuscular vaccination in the deltoid muscle with most published reports involving influenza vaccines. To estimate the risk of subdeltoid bursitis, a team of investigators performed a retrospective cohort study using The Vaccine Safety Datalink. This database contains health encounter data for 10.2 million members of 7 US health care organizations.
The cohort included 2,943,493 persons who underwent vaccination with an inactivated influenza vaccine during the 2016 to 2017 influenza season. Potential incident cases were identified by searching administrative data for those with a shoulder bursitis diagnostic code within 180 days after receiving an injectable influenza vaccine in the same arm. A self-controlled risk interval analysis was then used to calculate the incidence rate ratio of bursitis in a risk interval of 0 to 2 days after vaccination vs a control interval of 30 to 60 days, which represented the background rate.
The investigators identified 16 cases of symptom onset in the risk interval and 51 cases of symptom onset in the control interval. Within the risk interval, 69% of patients were women and the median age was 57.5 years (range, 24- 98 years). The incidence rate ratio was 3.24 (95% CI, 1.85-5.68), and the attributable risk was 7.78 (95% CI, 2.19-13.38) additional cases of bursitis per 1 million persons vaccinated.
Potential study limitations include the use of bursitis diagnostic codes to find cases, followed by confirmation through chart review. Although this process was implemented to increase specificity, it may have lacked sensitivity and led to an underestimation of risk. Also, the investigators cautioned that generalizations to intramuscular vaccinations other than for influenza “should be done with caution and represents a direction for future research.” Furthermore, generalizations to other vaccination settings in relation to staff training or quality control measures may not be possible.
In an editorial also published in the Annals of Internal Medicine,2 the authors stress that vaccination still provides critical protective value and offer some suggestions based on the findings available regarding bursitis following vaccination. As administration technique appears to play a role in shoulder injury, they suggest that medical practitioners might benefit from an injection technique “tune-up” and offer details on determining correct needle placement and length.
The editorial authors further caution that the ongoing coronavirus pandemic will likely increase the need to provide vaccinations in nontraditional settings. To help address this, they recommend that, “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.” According to the authors, simply, unbuttoning the first couple buttons of a long sleeve shirt will not work.
- Hesse EM, Navarro RA, Daley MF, et al. Risk for subdeltoid bursitis after influenza vaccination: a population-based cohort study [published online June 23, 2020]. Ann Intern Med. doi:10.7326/M19-3176
- Fryhofer SA, Fryhofer GW. Vaccination-induced bursitis: technique matters [published online June 23, 2020]. Ann Intern Med. doi:10.7326/M20-3302