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Increased Risk of Subcutaneous Nodules and Lipomas Following Influenza Vaccination: A Multicenter TriNetX Cohort Study

October 2025 | Volume 24 | Issue 10 | 8989 | Copyright © October 2025


Published online September 30, 2025

Neal Gupta MDa,b, Alexia Collins BSa,b, Kayla Zafar BAa,c, Maile Ray DSc MPHd, Sandra McGinnis PhDd, Marc Cohen MDa,b, Sharon Glick MDa,b, Jared Jagdeo MD MSa,b

aDermatology Service, Veterans Affairs New York Harbor Healthcare System - Brooklyn Campus, Brooklyn, NY
bDepartment of Dermatology, State University of New York, Downstate Health Sciences University, Brooklyn, NY
cSt. George’s University School of Medicine, Grenada, West Indies
dData Management and Analytics Center, State University of New York, University at Albany, Albany, NY
eRowan University School of Osteopathic Medicine, Stratford, NJ

Abstract
Background: Influenza vaccination represents one of the most widespread public health interventions. Localized cutaneous reactions, including nodules and pruritus, may occur rarely following vaccination, particularly when administered improperly. Our clinic observations suggest the potential development of lipomas following intramuscular vaccination.
Objective: This study evaluates the risk of subcutaneous nodules and lipoma development in the upper arm after intramuscular influenza vaccination.
Methods: We utilized the TriNetX platform to assess the risk of a subcutaneous nodule on the arm and lipoma development in patients who received intramuscular formulations of the annual influenza vaccine compared to those who never received the vaccine. A propensity score-matched cohort analysis was conducted to adjust for potential confounders.
Results: Our analysis demonstrated that individuals who received influenza vaccines were at an increased risk of developing a subcutaneous nodule of the arm, with a hazard ratio (HR) of 1.32 [95% confidence interval (CI): 1.28-1.37], or a lipoma of the upper arm, with an HR of 1.57 [95% CI: 1.28-1.93].
Conclusions: Intramuscular influenza vaccination administration is associated with an elevated risk of subcutaneous nodule and lipoma development in the upper arm. These findings highlight the importance of proper vaccine administration techniques to minimize adverse events.

INTRODUCTION

Subcutaneous nodules are a potential adverse event following immunization, which can cause discomfort and pruritus.1 A randomized trial in pediatric patients demonstrated that incorrect injection techniques can cause accidental subcutaneous delivery, leading to nodule formation.2 Influenza vaccines are among the most important vaccine interventions in the adult population.3 While limited evidence has linked influenza vaccines specifically to nodule formation, the similarity in administration technique raises the possibility of such an association. Traumatic injury to the subcutaneous tissue can also result in the formation of lipomas.4 These benign tumors are frequently encountered in the clinical setting, although the exact mechanism of their formation remains unknown.5 In our clinical practice, we have also noted the development of both subcutaneous nodules and lipomas following intramuscular influenza vaccination. We hypothesize that influenza vaccination increases the incidence of subcutaneous nodules and lipomas. To test this hypothesis, we conducted a retrospective cohort study using the TriNetX Research Network to evaluate the incidence of subcutaneous nodules and lipomas following influenza vaccination.

Study Sample
This retrospective cohort study used TriNetX, a global database of de-identified electronic health records (EHRs) from over 92 participating healthcare organizations and over 100 million patient charts covering diverse healthcare regions and settings from 2003 to 2024. To identify patient populations, TriNetX utilizes the International Classification of Diseases, Tenth Revision (ICD-10), Current Procedural Terminology (CPT), RxNorm, and Anatomical Therapeutic Chemical (ATC) codes. In our primary analysis, we identified an exposed cohort consisting of patients aged 12-75 years old who received at least 3 annual doses of
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