Radiologists around the country are noting a potential aftereffect of the COVID-19 vaccine: swelling in lymph nodes under the armpit that are showing up on mammograms.

Lymph nodes exist in various regions around the body, including the neck, groin and armpits, and swell in the presence of bacteria, infection or sometimes cancer, according to the Mayo Clinic.

Typically, an enlarged lymph node in the armpit region would warrant a biopsy of the breast tissue, as it can be an indicator of breast cancer that is beginning to spread, according to the Susan G. Komen Foundation; however, radiologists say that these occurrences after receiving the COVID-19 vaccine are to be expected and are not normally of concern.

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In most patients, evidence of swollen lymph nodes following vaccination typically does not warrant further action unless the swelling persists or other health issues are at play, Massachusetts General Hospital said in a recent release.

The Centers for Disease Control and Prevention noted in its Moderna and Pfizer vaccine reports that swelling of the lymph nodes was “plausibly related to the vaccine” and was most often witnessed in the arm and neck regions two to four days after vaccination. Swelling tended to last for an average of one to two days for Moderna and approximately 10 days for Pfizer.

Massachusetts General Hospital warned that radiologists would likely see an uptick in the number of enlarged lymph nodes showing up during mammograms as nationwide vaccination efforts increase.

Constance Lehman, chief of breast imaging at Massachusetts General Hospital, told The New York Times she’s glad word of this occurrence is spreading to help put people at ease.

“I am particularly eager to get the word out to all the patients undergoing surveillance after successful prior treatment of cancer,” she said.