Unilateral axillary adenopathy in patients recently vaccinated against COVID-19


Several national mammography commissions, societies, and associations concerned with diagnostic radiology and imaging are making recommendations based on consultations with patients with axillary lymphadenopathies or reactive lymphadenitis who have recently received COVID-19 vaccinations. 

According to these organizations, after the start of the COVID-19 vaccination campaigns, reactive lymphadenitis (enlarged axillary lymph nodes in women) is occurring more frequently in vaccinated women. In several of the cases, procedures ranging from biopsies to additional imaging have been recommended.

Clinical studies of several of the approved vaccines highlighted the possibility of axillary node enlargement on palpation, with varying frequency, depending on the vaccine. For the Moderna vaccine, this effect has been seen in 11% of first-dose cases, and in 16% of cases after the second dose, occurring more frequently in young people, in the armpit on the side where the vaccination was administered. These events are less common with the Pfizer and AstraZeneca vaccines. The CDC has indicated that enlargement of the axillary node on palpation on the side where the vaccination was administered is the second-most common local adverse side effect. When lymph nodes become swollen, this generally begins on the second day after vaccination, persists for at least 10 days, and can be detected in diagnostic imaging for several weeks. 

Given the possibility of these events occurring, especially in women, the following measures are recommended:

  • It should be emphasized that swollen lymph nodes after vaccination is an expected event and is not unique to COVID-19 vaccines, as it is also seen with other vaccines such as influenza, human papilloma, measles, chickenpox, and BCG – vaccines that induce a strong immune response.
  • Patients should not be alarmed if, within a few days of being vaccinated, lumps are noticeable in the armpits or neck, generally on the side where the vaccination was administered.
  • No specific medical care or diagnostic imaging is considered indicated unless the enlargement of the nodes persists for more than six weeks with no apparent decrease in size.
  • For patients with a personal history of breast cancer, it is recommended that the vaccine be administered on the side opposite to the side on which any medical intervention has occurred.
  • For programs for early detection of breast cancer, it is recommended that detailed information on vaccination history, type of vaccine, vaccination date, and side where the vaccine was administered be recorded.


Alvarez Benito M, et al. Recomendaciones de la Sociedad Española de Diagnóstico por Imagen de la Mama (SEDIM) para el manejo de mujeres con antecedente de vacunación para covid-19 reciente. [Recommendations of the Spanish Society of Breast Imaging (SEDIM) for the management of women with a recent history of COVID-19 vaccination.]  

Lehman CD, Lamb LR, D'Alessandro HA. Mitigating the Impact of Coronavirus Disease (COVID-19). Vaccinations on

Patients Undergoing Breast Imaging Examinations: A Pragmatic Approach. American Journal of Roentgenology, 2021, doi: 10.2214/AJR.21.25688

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