Risk of Shoulder Injury Related to Vaccine Administration for COVID-19 and Influenza Vaccinations
Chengyi Zheng, Lei Qian, Lina S. Sy, Gabriella V. Goodwin, Meiyu Yeh, Ronald A. Navarro, Dawn T. Asamura, Denison S. Ryan, Jonathan Duffy, Jennifer C. Nelson, Bruno J. Lewin, Hung Fu TsengImportance
The National Academies of Sciences, Engineering, and Medicine identified a critical evidence gap regarding the risk of shoulder injury related to vaccine administration (SIRVA) after COVID-19 vaccination.
Objective
To compare the risk of SIRVA after COVID-19 vs influenza vaccinations in adults.
Design, Setting, and Participants
This population-based cohort study included individuals aged at least 18 years who received a COVID-19 or influenza vaccination administered via intramuscular deltoid injection between August 1, 2023, and April 30, 2024, at Kaiser Permanente Southern California. Data were analyzed from June 2024 to September 2026.
Exposure
Receipt of COVID-19 vaccination or influenza vaccination.
Main Outcomes and Measures
The primary outcome was incident SIRVA, defined as shoulder symptoms beginning at or before 7 days and persisting more than 30 days after vaccination, identified using a validated natural language processing algorithm. Incidences were calculated per 10 000 vaccinations. Adjusted relative risks (RRs), risk differences, and 95% CIs were estimated using robust Poisson regression with inverse probability of treatment weighting.
Results
A total of 1 366 362 individuals (mean [SD] age at vaccination, 58.4 [18.2] years; 782 994 female [57.3%]) across 1 901 588 vaccinations were included (1 076 609 vaccinations [56.7%] were administered to females). Among 1 830 636 vaccinations in the primary analysis, 252 SIRVA cases were identified as follows: 110 cases (0.018%) after 596 614 COVID-19 vaccinations and 142 cases (0.012%) after 1 234 022 influenza vaccinations. An additional 13 SIRVA cases (0.018%) were identified among 70 952 simultaneous COVID-19 and influenza vaccinations. Most COVID-19 vaccines were Pfizer-BioNTech messenger RNA (667 455 of 667 566 [99.98%]), and influenza vaccines were predominantly standard-dose (866 530 of 1 304 974 [66.40%]) or high-dose (438 183 of 1 304 974 [33.58%]) inactivated quadrivalent formulations. SIRVA incidence was higher after COVID-19 than influenza vaccination, at an incidence of 1.84 (95% CI, 1.53-2.22) vs 1.15 (95% CI, 0.98-1.36) per 10 000 vaccinations, corresponding to an adjusted absolute increase of 0.67 cases (95% CI, 0.15-1.19) per 10 000 vaccinations (adjusted RR, 1.63; 95% CI, 1.16-2.28). Among adults 65 years or older, SIRVA incidence was 2.11 (95% CI, 1.67-2.67) per 10 000 for COVID-19 vaccination and 1.63 (95% CI, 1.28-2.07) per 10 000 for high-dose influenza vaccination (adjusted RR, 1.41; 95% CI, 0.92-2.15).
Conclusions and Relevance
Results of this cohort study suggest that although SIRVA was rarely associated with both vaccines, COVID-19 vaccination was associated with approximately 7 additional cases per 100 000 vaccinations compared with influenza vaccination. Among adults aged 65 years or older, SIRVA risk did not differ significantly between COVID-19 and high-dose influenza vaccination. The small absolute risk of SIRVA should be considered alongside the established benefits of COVID-19 and influenza vaccination in preventing severe disease and hospitalization.