A 28-year-old female subject underwent US examination 2 days after receiving the second dose of Pfizer-BioNTech vaccine due to palpable left axillary lump and ipsilateral armpit pain (same side of vaccine injection). She also experienced fatigue and headache. US showed the presence of axillary lymph nodes (maximum diameter 14 × 9 mm) with preserved fatty hilum, but diffuse cortical thickening (10 mm) and vivid hilar and cortical vascularization. A soft consistence of the cortex was found at shear-wave elastography (mean values between 3.4 and 8.1 kPa). No pathological lymph nodes were found in ipsilateral supra and subclavicular lymph node stations as well as in lymph nodes contralateral to the site of vaccine injection. Follow-up US examination was performed after 4 weeks and a reduction of lymph node size (7 × 6 mm), cortical thickness (2.9 mm) and vascularization was found (Fig. ).
A 30-year-old woman with the onset of fever, myalgia and left armpit pain ipsilateral to vaccine injection after the first dose underwent US examination 5 days later. Multiple axillary lymphadenopathies (maximum diameter 15 × 10 mm) with round to oval shape, poor hilar representation, thickened cortex and increased vascularization at color-Doppler were found. No pathological lymph nodes were found in ipsilateral supra and subclavicular lymph node stations as well as in lymph nodes contralateral to the site of vaccine injection.\nUS follow-up performed 4 weeks later showed stable lymph node size with restored fatty hilum as well as reduced cortical thickness and vascularization (Fig. ).