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

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.

This study evaluates the risk of subcutaneous nodules and lipoma development in the upper arm after intramuscular influenza vaccination.

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.

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].

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.