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. ).
US examination was performed in a 33-year-old woman with the occurrence of axillary pain and a palpable lump in the supraclavicular region 8 days after the first dose of Pfizer-BioNTech vaccine. The patient had also experienced fever and fatigue right after vaccine injection. Both axillary and supraclavicular lymph nodes were found enlarged (maximum diameter 14 × 6 mm), with no fatty hilum, increased vascularization and soft-intermediate consistence at shear-wave sonoelastography (Fig. ). No pathological lymph nodes were found in the contralateral axilla. US lymph node features were substantially stable at US examinations performed after 3 weeks.