A 28-year-old male asymptomatic subject underwent US examination for screening purpose 3 days after the second vaccine dose. A round hypoechoic axillary lymph node (13 × 20 mm) was found with increased vascular signal at color-Doppler examination at the same site of vaccine injection (left arm). An enlarged axillary lymph node was also detected (21 × 7 mm) with preserved hilar representation but diffuse cortical thickening (6 mm) and abnormal vascularization. Both lymph nodes showed soft consistence at shear-wave sonoelastography (mean values between 27 and 38 kPa). No pathological lymph nodes were found in both ipsilateral and contralateral supra/subclavicular and cervical stations as well as in the contralateral axilla. Both findings were no longer detectable at 4 weeks US examination (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. ).