Soon after the United States began rolling out experimental COVID-19 vaccines distributed under an Emergency Use Authorization (EUA), doctors began seeing an influx of female patients making mammogram appointments after the women experienced enlarged lymph nodes, known as axillary lymphadenopathy, in the armpit area after receiving a dose of mRNA COVID-19 vaccine.1
Laura Esserman, MD, Director of University of California San Francisco’s Breast Care Center said that their clinic is receiving an overwhelmingly large number of calls from women who have been given an mRNA COVID-19 vaccine, who are concerned that swollen lymph nodes in the armpit area maybe a sign of breast cancer.2 She said, “I’m sure hundreds of thousands of women across the country will be affected by this for sure.”3
Messenger RNA COVID-19 Vaccines Can Cause Enlargement of Lymph Nodes
According to Yale Medicine, swelling of the lymph nodes in the armpit was a recognized side effect in the clinical trials of the Moderna/NIAID and Pfizer/BioNTech COVID-19 vaccines.4 The New York Times reported that the Moderna study showed that “11.6 percent of patients reported swollen lymph nodes after the first dose, and 16 percent after the second dose. The Pfizer/BioNTech vaccine seems to have a lower incidence, with 0.3 percent of patients reporting it.”5
Lisa Mullen, MD, a radiologist at John Hopkins Medicine who specializes in breast imaging said:
Lymph nodes under the arm where a person has gotten a vaccine can become enlarged as part of the normal immune response to the vaccine.6
Dr. Mullen says that enlarged lymph nodes in the armpits can occur after either the first or the second dose of the vaccine.7 She adds that not all vaccines cause swollen lymph nodes; however, the ones that cause a more intense immune response such as the COVID-19 vaccines, the shingles vaccines, the diphtheria/tetanus/pertussis vaccine, influenza vaccines and others, are more likely to affect lymph nodes. She also notes that getting multiple vaccines at the same time can cause enlarged lymph nodes as well.8
Enlarged Lymph Nodes from COVID-19 Vaccines Affecting Mammograms, CT Scans, MRIs and Ultrasounds
Medical professionals are witnessing enlarged lymph nodes on imaging scans such as mammograms, CT scans, MRIs, and ultrasounds. This has raised concerns among those unfamiliar with this side effect of the COVID-19 vaccine. This has been the case for some women who have had mammograms showing enlarged nodes that looks very similar to what could be an early sign of breast cancer.9
Constance Lehman, MD, PhD, Chief of Breast Imaging and co-director of the Avon Comprehensive Breast Evaluation Center at Massachusetts General Hospital said that as COVID-19 vaccination rates increase, radiologists should expect to see increasing numbers of patients with enlarged lymph nodes on imaging exams. They recommend that imaging centers document COVID-19 vaccination information on all patient forms and ensure that this information is easily available to radiologists at the time the image is interpreted.10
In cases where the patient has recently received the COVID-19 vaccine, no additional imaging tests are needed for swollen lymph nodes unless the swelling persists or if the patient has other health concerns.11
Brita Roy, MD, MPH, an internal medicine physician and director of population health for Yale Medicine said:
At Yale, we have been talking to our breast radiologists and the national radiology associations. Ideally, you would not have a mammogram scheduled within a month of receiving your last dose of an mRNA vaccine. However, if schedules are full, postponing it might mean having to go a very long time. So, if it’s possible to have your mammogram done before you are vaccinated, that’s ideal.12
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1 Pena L. Vaccine side effects: Why women are mistaking swollen lymph nodes for breast cancer. ABC Chicago May 4, 2021.
4 MacMillan C. Medical Experts Spread Word About Harmless COVID-19 Vaccine Reactions. Yale Medicine Mar. 30, 2021.
5 Grady D. A Covid Vaccine Side Effect, Enlarged Lymph Nodes, Can Be Mistaken for Cancer. The New York Times Mar. 1, 2021.
6 Mullen LM. COVID-19 Vaccine: Can It Affect Your Mammogram Results? Hopkins Medicine Mar. 29, 2021.
9 MacMillan C. Medical Experts Spread Word About Harmless COVID-19 Vaccine Reactions. Yale Medicine Mar. 30, 2021.
10 Lamb L, Lehman C. The implications of swollen lymph nodes following COVID-19 vaccination. Mass General Mar. 2, 2021.
12 MacMillan C. Medical Experts Spread Word About Harmless COVID-19 Vaccine Reactions. Yale Medicine Mar. 30, 2021.