Could your COVID vaccine affect the results of your next mammogram?

Potential, temporary side effects after a COVID-19 vaccination have been well documented. Some people may experience soreness or pain at the injection site, fatigue, a slight fever, chills, nausea, body aches, or headache.

A lesser-known effect is swollen lymph nodes in the armpit area. They aren’t typically a cause for concern, and in fact, harmless swelling is a normal response for many people. It’s a sign that your lymph nodes are doing their job and stimulating your immune system to protect you from the coronavirus that causes the disease.

But, while there is no link between COVID vaccines and breast cancer, swelling could raise a false alarm when it appears on imaging tests—especially routine mammograms.

Why do lymph nodes swell?

Lymph nodes contain white blood cells that fight infection. Underarms contain a cluster of about 20 to 40 lymph nodes. When the immune system detects the presence of a potentially harmful substance, such as bacteria, viruses, chemicals, or pollen, it increases white blood cell production. This can also happen with some vaccines.

The white blood cells attack the foreign substance, leading to swollen lymph nodes. You might even feel a tender lump or swelling in your armpit. The lump or swelling should go away within a few days or weeks. If it doesn’t, let your healthcare provider (HCP) know.

When lymph nodes under the arms appear larger than normal on a screening exam like a mammogram, they can sometimes indicate the presence of breast cancer or other cancers like lymphoma and leukemia. Unfortunately, radiologists can’t discern the cause of swollen lymph nodes under the arms (called axillary lymphadenopathy) that appear on your mammogram. So, additional imaging tests may be needed.

Initial precautions around vaccine timing

During the pandemic, some health organizations, such as the Society of Breast Imaging (SBI), recommended that women schedule a mammogram before their first COVID shot, or wait for several weeks after the second dose. The goal was simple: Avoid unnecessary worry from a mammogram that looked abnormal due to vaccine-related swelling.

But, as time passed, HCPs learned more about that swelling. Up to 35 percent of women experienced it, and it could last as long as 43 weeks, according to a 2022 study in Radiology. Many HCPs worried women would postpone mammograms, causing delays in diagnosis and treatment of breast cancers.

Based on this clearer understanding, guidance changed. Today, health organizations like the SBI no longer advise delaying screening mammograms around COVID vaccinations.

Follow-up exams for swollen lymph nodes

What happens if you undergo a mammogram shortly after your vaccination and you have swollen lymph nodes? If there are no other suspicious findings, you likely won’t be called back for additional screening.

In some cases, you may need further evaluation, says Lisa A. Mullen, MD, an assistant professor of radiology in the Breast Imaging Division of Johns Hopkins University School of Medicine. In this situation, you’ll usually have an underarm ultrasound to look more closely at the lymph nodes and measure their size.

You’ll then need to return sometime after your ultrasound to see whether your lymph nodes have calmed down. “For a totally healthy asymptomatic woman,” Mullen adds, “we’re recommending a follow-up in three months.”

Recalls can be anxiety-producing for patients, Mullen says. “Patients are worried that we’re seeing breast cancer. But all we’re seeing is a big lymph node because of their vaccine. But we’re obligated to treat it as if it could be a sign of breast cancer.”

“If a patient has any symptoms at all that she’s worried about that relate to her breast or underarms, such as a breast lump, breast pain or nipple discharge, she should talk to her HCP, Mullen advises. “She should not delay any type of evaluation. It could be that it’s COVID vaccine-related. But if we don’t know, it’s not good to assume.”

Before you’re screened, tell your healthcare provider and mammogram technologist that you were recently immunized against COVID and in which arm the vaccine was injected. If the radiologist sees swelling, it could help with the interpretation of your results, and you might be able to avoid unnecessary follow-up testing.

Get screened regularly

If you’ve skipped your annual mammogram, it’s important to schedule one as soon as possible.

Most organizations like the American Cancer Society and the U.S. Preventive Services Task Force publish guidelines that advise women with an average breast cancer risk to start annual screenings at age 40 to 50. Specific recommendations are as follows:

• American Cancer Society (ACS): Women can start screening between ages 40 and 45 if they so choose. Beginning at 45, the ACS recommends annual mammograms. At 55, getting screened every one or two years is recommended if you’re healthy and expect to live at least another 10 years.
• American College of Obstetricians and Gynecologists (ACOG): Women at average risk of breast cancer should be screened every one or two years starting at age 40.
• National Comprehensive Cancer Network (NCCN): Yearly mammograms should start at 40.
• United States Preventive Services Task Force (USPSTF): Between 40 and 74, women should have mammograms every other year.

Talk with your HCP to determine the best screening schedule for you.