Being fully vaccinated against COVID-19 and getting regular mammograms are both important and can save lives, but one harmless, temporary side effect of the vaccines can affect your mammogram results. Swollen lymph nodes in the armpit are a normal immune response to the shot, but this can also be a symptom of breast cancer. Sarah Deitch, MD, breast radiologist, explains how vaccines may affect mammogram results and how swollen lymph nodes in the armpit are diagnosed.

Swollen Lymph Nodes in the Armpit Can be a Normal Immune Response to a COVID Vaccine

Lymph nodes are glands throughout the body that make up the lymphatic system, which is responsible for the body’s immune response. They play an important role in preventing infection and destroying harmful bacteria or viruses. Usually, temporarily swollen or enlarged lymph nodes are not a cause for concern and simply indicate the body is defending itself from an invader.

“Swollen lymph nodes from a vaccine typically return to normal within a few days to a few weeks,” Dr. Deitch said.

All three COVID vaccines, Pfizer-BioNTech, Moderna and Johnson & Johnson can temporarily cause swollen lymph nodes in the armpit. This can happen after the first or second dose. The swelling is in the underarm because the lymph nodes in the armpit are closest to the injection site. Immune reactions are more intense with the COVID vaccines, but lymph nodes can also swell with other vaccines, such as the shingles vaccine.

Wait Four Weeks Between Your COVID Vaccine and Your Mammogram

There is no link between breast cancer and the COVID vaccines. However, because swollen lymph nodes in the armpit are a known side effect of the vaccines, the CDC recommends a waiting period of at least four weeks for most women between vaccination and a mammogram. It is important to let your mammography technologist know the date of your COVID vaccine and the arm in which you received the shot.

“If enlarged lymph nodes are seen on your screening mammogram, we may ask you to return for additional imaging,” Dr. Deitch said. “Often, mildly enlarged lymph nodes can be evaluated with a follow-up ultrasound to ensure that they have returned to normal size.”

Some people, including those who are experiencing breast symptoms, such as a lump, should not wait to schedule a diagnostic mammogram.

Your Mammogram Shows Swollen Lymph Nodes in the Armpit. Now What?

If you are asked to return for additional imaging, this may include an ultrasound of the underarm. The purpose of the ultrasound is for the radiologist to gather more information and data about the lymph nodes.

“The ultrasound allows us to measure the outside rim or cortex of a lymph node,” Dr. Deitch said. “Abnormal cortical thickness can be a sign of a reactive lymph node due to an immune response to a vaccine or a symptom of cancer. Additional features can indicate how suspicious a lymph node is, such as the overall shape and abnormal blood flow to the lymph node, as well as other findings in the breast.”

Your radiologist may also recommend a biopsy if the lymph node remains enlarged with abnormal cortical thickening or if there are any other concerning findings in the breast.

The Bottom Line: COVID Vaccines and Mammograms Save Lives

Screening mammograms are proven as the best way to detect breast cancer because they can find cancer when it is too small for you to feel. When found early, breast cancer is very treatable, and there are better chances for a good outcome. According to the National Cancer Institute, finding breast cancer when it is still contained within the breast gives you a 99% chance of survival. If the cancer is discovered when it has already spread to other organs, the long-term survival rate is 29%.

“Do not delay your flu or COVID vaccines — or your annual mammogram,” Dr. Deitch said. “With proper planning and timing, vaccines and breast cancer screening play an important role in your health, and both save lives.”

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