Shoulder conditions not uncommon after vaccinations

Intramuscular vaccination in the deltoid muscle is associated with a small absolute risk for shoulder conditions, suggests a recent study.

Members of the Kaiser Permanente Southern California, a large integrated healthcare organization, who are ≥3 years of age and had an intramuscular vaccination administered in the deltoid muscle between 1 April 2016 and 31 December 2017 were included in this retrospective cohort study.

The authors identified potential shoulder conditions among vaccinated persons with shoulder disorder diagnosis codes using a natural language processing (NLP) algorithm. All NLP-identified cases were manually chart-confirmed based on case definition. Finally, the authors compared characteristics of vaccinated persons with and without shoulder conditions.

A total of 3,758,764 vaccinations were administered, of which 374 shoulder conditions occurred, with an estimated incidence of 0.99 (95 percent confidence interval [CI], 0.89‒1.09) per 10,000 vaccinations. The incidence for adult and paediatric populations was 1.22 (95 percent CI, 1.10‒1.35) and 0.05 (95 percent CI, 0.02‒0.14), respectively.

In the adult vaccinated population, the following factors correlated with an increased risk for shoulder conditions: advanced age, female sex, an increased number of outpatient visits in the 6 months prior to vaccination, lower Charlson Comorbidity Index, and pneumococcal conjugate vaccine.

Among influenza vaccines, quadrivalent ones appeared to increase the risk for shoulder conditions. In addition, simultaneous administration of vaccines contributed to a higher risk for shoulder conditions among older adults.

“Given the high burden of shoulder conditions, clinicians should pay attention to any factors that may further increase risks,” the authors said.

The study had certain limitations, including generalizability to other healthcare settings, use of administrative data, and residual confounding.