Shoulder injury related to vaccine administration occurs more frequently following COVID-19 shots than after influenza vaccinations, according to a study published November 4, 2026, in JAMA Internal Medicine, Medscape reported. The analysis tracked over 1.8 million injections and found about 7 additional cases per 100,000 doses for the COVID-19 vaccine compared to the flu shot.
What did the study examine?
Researchers conducted a retrospective analysis of adults who received vaccinations between August 2023 and April 2024 at Kaiser Permanente Southern California facilities. The study utilized a validated natural language processing algorithm to identify cases of shoulder injury related to vaccine administration, commonly known as SIRVA. Investigators evaluated 1,234,022 influenza vaccinations and 596,614 COVID-19 vaccinations after excluding simultaneous same-day, same-arm injections from their primary analysis, according to data detailed by AJMC.
The total study population included 1,366,362 individuals across 1,901,588 total vaccinations, with a mean age of 58.4 years. Female patients accounted for 57.3% of the cohort. Among the eligible vaccinations, 37.0% were received by Hispanic individuals, 35.1% by White individuals, 16.5% by Asian or other Pacific Islander individuals, 7.1% by Black individuals, and 4.3% by individuals of multiple, other, or unknown race and ethnicity.
How did SIRVA rates compare?
SIRVA incidence reached 1.84 cases per 10,000 COVID-19 vaccinations, compared with 1.15 cases per 10,000 influenza vaccinations. This yielded an adjusted relative risk of 1.63, or approximately 7 additional cases per 100,000 doses, according to the findings. Out of 252 total identified cases, 110 occurred after a COVID-19 vaccination and 142 followed a flu shot.
Among adults aged 65 years or older, researchers observed no significant difference in SIRVA risk when comparing COVID-19 vaccination to a high-dose inactivated quadrivalent influenza vaccine, which is a standard recommendation for older populations. However, COVID-19 vaccination carried a higher risk than a standard-dose influenza vaccine in this age group, though that comparison involved only 9 cases among standard-dose recipients.
What are the study limitations?
Case identification relied heavily on patients seeking medical attention and on clinical documentation within a single health system. This design may underestimate the true incidence of SIRVA.
Investigators noted that the single-system design at Kaiser Permanente Southern California and the use of predominantly Pfizer-BioNTech mRNA COVID-19 vaccines may limit the generalizability of the findings to other populations. Unmeasured factors such as needle length, precise injection site within the deltoid muscle, and pre-existing undiagnosed shoulder conditions could also introduce residual confounding.
Why do researchers emphasize training?
The specific term “SIRVA” appeared in the medical records of only 7 out of 265 confirmed cases, representing just 2.6% of the total. Study authors pointed out that this infrequent documentation highlights a need for greater clinical awareness.
The infrequent documentation underscores the need for greater clinician and patient awareness to facilitate timely evaluation and management,
the authors wrote in the study.
Continued competency-based training in anatomical landmarking and individualized needle selection may reinforce recommended administration practices.
Despite these findings, the study team concluded that the preventive benefits of both immunizations outweigh the risks. The benefits of COVID-19 and influenza vaccination in preventing severe disease and hospitalization may outweigh the small absolute risk of SIRVA,
the researchers stated.
Questions about the research presentation and funding
When and where was the research presented?
The study was presented on November 3, 2026, at the American Public Health Association Annual Meeting in San Antonio, Texas, prior to its online publication in JAMA Internal Medicine on November 4, 2026.
Who funded the investigation?
The research received support from a contract awarded by the Centers for Disease Control and Prevention through the Vaccine Safety Datalink. The agency participated in study design, data interpretation, and manuscript review.
What types of influenza vaccines were administered?
Among the influenza vaccines included in the final analysis, 66.40% were standard-dose inactivated quadrivalent influenza vaccines and 33.58% were high-dose inactivated quadrivalent influenza vaccines.