New research highlights key factors associated with the resolution of reactive lymphadenopathy visualized on breast imaging after patients receive an mRNA COVID vaccine. 

“The variable clinical course of subclinical lymphadenopathy detected on breast imaging after COVID-19 vaccination creates management challenges and has led to evolving practice recommendations,” corresponding author Michele B. Drotman, MD, from the Department of Radiology at Weill Cornell Medicine, and co-authors explained. 

Vaccine-related lymphadenopathy is a well-documented side effect of mRNA COVID vaccines but, until recently, little was known about the specifics pertaining to its clinical course and resolution. A new study published in the American Journal of Roentgenology this week confirmed prior findings that indicated the reactive inflammation is benign in nature and can take weeks to resolve, and also took the research a step further by characterizing features that are associated with the amount of time it takes for the side effect to fully subside. 

This involved retrospectively assessing 111 women who experienced axillary lymphadenopathy ipsilateral to either a Pfizer or Moderna COVID vaccine. After the findings were initially detected via ultrasound (within 8 weeks of inoculation), the women underwent follow-up ultrasound imaging in 4 to 12 week intervals until the lymphadenopathy resolved. 

The researchers found the reactive inflammation subsided 127±43 days after the first vaccine dose and 97±44 days after the initial ultrasound. Significant associations between shorter resolution times and Pfizer vaccinations were observed (compared to Moderna vaccination) in addition to longer resolution times for the women who received their second vaccine dose after having already developed lymphadenopathy.