Axillary Lymphadenopathy After a COVID-19 Vaccine Booster Dose: Time to Resolution on Ultrasound Follow-Up and Associated Factors.

Background: Given ongoing administration of booster doses of COVID-19 vaccines, radiologists are continuing to encounter COVID-19 vaccine-related axillary lymphadenopathy on imaging. Objective: The purpose of this study was to assess the time to resolution of COVID-19 vaccine-related axillary lymphadenopathy identified on breast ultrasound after a booster dose, and to assess factors potentially associated with the time to resolution. Methods: This retrospective single-institution study included 54 patients (mean age, 57 years) with unilateral axillary lymphadenopathy ipsilateral to a booster dose of mRNA COVID-19 vaccine visualized on ultrasound (whether an initial breast imaging examination or follow-up to prior screening or diagnostic breast imaging) performed between September 1st, 2021, and December 31st, 2022, and who underwent follow-up ultrasound examinations until resolution of lymphadenopathy. Patient information was extracted from the EMR. Univariable and multivariable linear regression analyses were used to identify predictors of time to resolution. Time to resolution was compared with a previously published sample of 64 patients from the study institution that was used to evaluate the time to resolution of axillary lymphadenopathy after the initial vaccine series. Results: A total of 6/54 patients had a history of breast cancer; 2/54 patients had symptoms related to the axillary lymphadenopathy (axillary pain in both patients). The initial ultrasound examinations showing the lymphadenopathy comprised 33/54 screening ultrasound examinations and 21/54 diagnostic ultrasound examinations. The lymphadenopathy resolved a mean of 102±56 days after the booster dose and 84±49 days after the initial ultrasound showing the lymphadenopathy. Age, vaccine booster type (Moderna vs Pfizer), and history of breast cancer were not significantly associated with time to resolution in univariable or multivariable analyses (all p>.05). Time to resolution after a booster dose was significantly shorter than the time to resolution after the first dose of the initial series (mean, 129±37 days) (p=.01). Conclusion: Axillary lymphadenopathy after a COVID-19 vaccine booster dose has a mean time to resolution of 102 days, shorter than the time to resolution after the initial series. Clinical Impact: The time to resolution after a booster dose supports the current recommendation for a follow-up interval of at least 12 weeks for suspected vaccine-related lymphadenopathy.