Risk for Shoulder Conditions After Vaccination: A Population-Based Study Using Real-World Data

Background: Although shoulder conditions have been reported as an adverse event after intramuscular vaccination in the deltoid muscle, epidemiologic data on shoulder conditions after vaccination are limited. Objective: To estimate the risk for shoulder conditions after vaccination and assess possible risk factors. Design: Retrospective cohort study. Setting: Kaiser Permanente Southern California, a large integrated health care organization. Participants: Kaiser Permanente Southern California members aged 3 years or older who had an intramuscular vaccination administered in the deltoid muscle between 1 April 2016 and 31 December 2017. Measurements: A natural language processing (NLP) algorithm was used to identify potential shoulder conditions among vaccinated persons with shoulder disorder diagnosis codes. All NLP-identified cases were manually chart confirmed on the basis of our case definition. The characteristics of vaccinated persons with and without shoulder conditions were compared. Results: Among 3 758 764 administered vaccinations, 371 cases of shoulder condition were identified, with an estimated incidence of 0.99 (95% CI, 0.89 to 1.09) per 10000 vaccinations. The incidence was 1.22 (CI, 1.10 to 1.35) for the adult (aged >= 18 years) and 0.05 (CI, 0.02 to 0.14) for the pediatric (aged 3 to 17 years) vaccinated populations. In the adult vaccinated population, advanced age, female sex, an increased number of outpatient visits in the 6 months before vaccination, lower Charlson Comorbidity Index, and pneumococcal conjugate vaccine were associated with a higher risk for shoulder conditions. Among influenza vaccines, quadrivalent vaccines were associated with an increased risk for shoulder conditions. Simultaneous administration of vaccines was associated with a higher risk for shoulder conditions among elderly persons. Limitation: Generalizability to other health care settings, use of administrative data, and residual confounding. Conclusion: These population-based data suggest a small absolute risk for shoulder conditions after vaccination. Given the high burden of shoulder conditions, clinicians should pay attention to any factors that may further increase risks. Primary Funding Source: Centers for Disease Control and Prevention. Ann Intern Med. doi:10.7326/M21-3023 Annals.org For author, article, and disclosure information, see end of text. This article was published at Annals.org on 22 March 2022.