Axillary Adenopathy Secondary to SARS-CoV-2 Vaccination: a Case Report

SARS-CoV-2 mRNA vaccines are safe and effective for the prevention of COVID-19 infection, though local reactions are commonly reported. Axillary lymphadenopathy has also been reported, which has the potential of causing diagnostic confusion and unnecessary testing and procedures. A 58-year-old female with untreated latent tuberculosis was noted to have a pulmonary nodule on chest radiograph. Evaluation for Mycobacterium tuberculosis was undertaken, and a FDG PET/CT was performed to rule out malignancy. While the nodule demonstrated low avidity, highly avid lymph nodes were noted in the left axillary region. Further questioning elicited a recent history of mRNA-1273 (Moderna) COVID-19 vaccination in her left deltoid muscle 3 weeks prior and a sensation of axillary fullness. She was managed conservatively with spontaneous resolution of her lymphadenopathy. Axillary lymphadenopathy following mRNA vaccination has been reported and appears to be more common with mRNA-1273 (Moderna) than BNT162b2 vaccine (Pfizer-BioNTech), in those aged 18 to 64 as compared to age ≥ 65, and following the second vaccine dose compared to the first dose. Vaccination should be considered in the differential diagnosis of axillary lymphadenopathy, particularly ipsilateral to the vaccination site, to avoid unnecessary testing, treatment, and patient anxiety.