Mammogram May Show Swollen Lymph Nodes From COVID-19 Vaccine

February 15, 2021

If you’ve received the COVID-19 vaccine and later feel a new lump or tenderness under your arm, near your armpit or on your neck, you might be worried that you’ve found cancer.

But you can put that worry firmly aside – at least for a couple of weeks, says radiology-breast imaging specialist Holly Marshall, MD. Dr. Marshall is Division Chief, Breast Imaging at UH Cleveland Medical Center.

Physicians are learning that the two COVID-19 vaccines currently in use can cause your lymph nodes to swell on the same side where you received the shot.

Those lumps are in response to COVID-19 vaccine, Dr. Marshall says. They indicate that your body is marshalling its powers to fight the perceived intruder – exactly what is supposed to happen following inoculation. However, this does not happen to everyone, as everyone is different, she says.

“It’s a normal occurrence while your body is building an immune response to fight the virus,” Dr. Marshall says. “The swelling may be a sign that the body is making antibodies in response to the vaccine as intended.”

Case Studies

Since COVID-19 vaccinations started in December, radiologists started noticing swollen lymph nodes on mammograms and other imaging studies, and then realized these patients had been recently vaccinated for COVID-19.

An article recently published in the journal Clinical Imaging described four case studies in which four women with no history of breast cancer had swollen lymph nodes. Some of the swollen lymph nodes could be felt, others were visible only through imaging that their doctors ordered.

All four had recently received their first dose of a COVID-19 vaccine in their upper arms a week to two weeks earlier. Three had received the Pfizer-BioTech vaccine; the fourth had received the Moderna vaccine.

A Side Effect

The U.S. Centers for Disease Control & Prevention (CDC) reports that 11.6 percent of vaccine recipients experienced swollen lymph nodes after one COVID-19 dose, and 16 percent after the second. Swelling typically appeared within two to four days after vaccination.

“Sometimes with other vaccines, occasionally we will see swollen lymph nodes, but it was unexpected how many swollen lymph nodes our breast radiologists have been seeing on screening mammograms of patients who have been vaccinated,” Dr. Marshall says.

Return To Normal

The lymph nodes should return to normal size anytime from a couple of weeks up to a month or two later, Dr. Marshall says.

If the swelling doesn’t go away in a couple months, talk with your doctor about getting the swelling examined.

“Wait a few weeks, and if there’s no change, then come in and we will evaluate it,” Dr. Marshall says.

If you undergo a screening mammogram after receiving COVID-19 vaccine, you might get called back for an ultrasound if your lymph nodes appear swollen on the scan, Dr. Marshall says. The follow-up ultrasound helps physicians ensure the swelling is not due to a malignancy.

And, Dr. Marshall says, getting the COVID-19 vaccine is not a reason to delay your mammogram.

“It’s still very important for women to get an annual mammogram starting at age 40,” she says. “Do not delay.”