Background: Shoulder injury from vaccination was approved for automatic compensation from the Vaccine Injury Compensation Program (VICP)-a federal government program started in 1988 to shield the manufacturers of childhood vaccines from liability. The approval was made on the basis of case reports rather than experimental evidence. This, combined with the addition of influenza vaccination to the VICP in 2005 (which broadened coverage to include adults) and other social factors, was associated with a rapid rise in the number of claims of shoulder injury from vaccination over the last decade, which now account for more than half of all claims to the VICP. Given the high prevalence of newly symptomatic sources of shoulder pain such as rotator cuff tendinopathy, combined with the high prevalence of annual influenza vaccinations, there is a substantial risk of overlap leading to the post hoc ergo propter hoc fallacy ("after this, therefore because of this") contributing to misdiagnosis and inappropriate management of patients that perceive injury from vaccination. Records of medical care after a large number of vaccinations have a good chance of detecting serious shoulder pathology, even it is uncommon, which would result in an increased prevalence of visits for shoulder problems and specific types of shoulder pathology.
Questions/purposes: Is there a difference in the proportion of visits for shoulder pain within 3 months before and after vaccination among students and faculty receiving an influenza vaccination in the shoulder?
Methods: We studied people who were vaccinated for influenza between 2009 and 2018 at a university health service. During the study period, a comprehensive billing database identified 24,206 influenza vaccinations administered to 12,870 people (median age 20 years, range 16-77; 57% women). We had 80% power to detect a 0.1% increase in the proportion of shoulder problems after vaccination compared with before vaccination. Visits with coded ICD-9 shoulder diagnoses were identified from the electronic medical record. We compared the proportion of shoulder evaluations within 3 months before and 3 months after vaccination.
Results: With the numbers available, the proportion of visits for shoulder problems were not different before (1.1% [52 of 4801]) and after vaccination (1% [40 of 3977], risk ratio 1.1 [95% CI 0.8 to 1.5]; p = 0.72). Among all vaccinations, 49% (11,834 of 24,206) were preceded or followed by an appointment within 3 months before (20% [4801 of 24,206]), after (16% ), or both before and after (13% ) vaccine administration, and 1.4% (170) of these visits were related to a shoulder issue. The most common reason for shoulder-related appointments was atraumatic shoulder pain (79% [134 of 170]).
Conclusions: Shoulder symptoms sufficient to seek care are notably common, even among relatively young adults, and are not more common after vaccination. Although this does not rule out an important rare pathology specific to vaccination, it seems important to consider the potential harms of assuming, based largely on chronology, that persistent shoulder pain after vaccination-something expected to be common based merely on the anticipated frequency of overlap of vaccination and common shoulder problems-represents harm from vaccine.
Level of evidence: Level III, therapeutic study.