MONDAY, March 21, 2022 (HealthDay News) — There is a small absolute risk for shoulder conditions after intramuscular vaccination administered in the deltoid muscle, according to a study published online March 22 in the Annals of Internal Medicine.

Chengyi Zheng, Ph.D., from Kaiser Permanente Southern California in Pasadena, and colleagues conducted a retrospective cohort study using a natural language processing algorithm to identify potential shoulder conditions among vaccinated persons with discharge codes for shoulder disorder. Participants were aged 3 years or older and had an intramuscular vaccination administered in the deltoid muscle between April 1, 2016, and Dec. 31, 2017.

The researchers identified 371 cases of shoulder conditions among 3,758,764 administered vaccinations, with an estimated incidence of 0.99 per 10,000 vaccinations. For the adult (aged 18 years or older) and pediatric (aged 3 to 17 years) vaccinated populations, the incidence was 1.22 and 0.05, respectively, per 10,000 vaccinations. Among vaccinated adults, the risk for shoulder conditions was increased in association with advanced age, female sex, an increased number of outpatient visits in the six months before vaccination, lower Charlson Comorbidity Index, and pneumococcal conjugate vaccine. Among influenza vaccines, the risk for shoulder conditions was increased with quadrivalent vaccination. Among elderly persons, simultaneous administration of vaccines was associated with a higher risk for shoulder conditions.

“Although shoulder conditions may be preventable if caused by inappropriate vaccine administration, this study was not able to determine their true cause,” the authors write. “More research is needed to better understand the risk factors and causal pathways for shoulder conditions after vaccination.”

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