Unilateral axillary adenopathy induced by COVID-19 vaccine: US follow-up evaluation.

Objectives: This study was conducted in order to investigate COVID-19 vaccine influence on unilateral axillary lymph nodes, comparing nodal basal features with their characteristics after the first and second vaccination dose.

Methods: Ninety-one volunteer employees from our center who participated in the BNT162b2 (Pfizer-BioNTech) vaccination campaign were prospectively recruited. A total of three axillary ultrasound evaluations of the ipsilateral vaccinated arm were performed: before vaccination, the week after the first dose and the week after the second dose. The following findings were recorded: the total number of visible nodes, the maximum measurements of the diameter and cortex, Bedi's classification, and color Doppler evaluation. The collected data were compared using paired-sample Student's t-test for quantitative continuous variables and Wilcoxon rank-sum test for ordinal variables. Additional analyses were performed after classifying patients according to the previous history of COVID-19 disease. Differences among both groups were evaluated with the Mann-Whitney U test. Variables with a p value < 0.05 were considered statistically significant.

Results: Comparative analyses between the three US examinations showed a statistically significant augmentation of total visible nodes, maximum diameter, cortical thickness, grade of Bedi's classification, and Doppler signal (p < 0.001). Analyses between patients with and without previous COVID-19 infection showed a higher lymph node response in naïve patients compared to those who were previously infected.

Conclusions: According to our results, both doses of COVID-19 vaccine induced an increase of all axillary lymph node parameters with statistically significant differences, especially in coronavirus-naïve patients.

Key Points: • Pfizer COVID-19 vaccine induces a high incidence of ipsilateral axillary lymphadenopathy. • US scan identified an increase of all lymph nodes parameters, especially in coronavirus-naïve patients.