You may want to reschedule your next mammogram if it falls too close to your vaccination appointment.

By Korin Miller
February 16, 2021
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A leading breast imaging organization in the country is recommending that women wait to schedule a mammogram until four weeks after their COVID-19 vaccine over concerns about an odd new side effect.

The Society of Breast Imaging (SBI) is warning that women who were recently vaccinated could have swelling and a lump in the lymph nodes of their armpit, which can be mistaken as a sign of breast cancer. The SBI issued the recommendation in a recently-released three-page document, which warns about the risk of the vaccine causing axillary adenopathy, aka a change in the size and consistency of lymph nodes in the armpit that can be a sign of breast cancer. (In the case of breast cancer, axillary adenopathy can be a signal that breast cancer has spread.)

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While the SBI says that axillary adenopathy is "rare" in general and "rarely reported' after HPV and flu vaccines, it also notes that women who have recently been vaccinated against COVID-19 may experience this.

The SBI cites data that found 11.6% of patients who received the Moderna COVID-19 vaccine had swelling or tenderness after receiving their second shot and that lymphadenopathy, i.e. swelling, happened in more than 1% of people in clinical trials. These symptoms were more rare in people who received the Pfizer-BioNTech COVID-19 vaccine, but they did happen.

Worth noting: The SBI guidance also says that the "true incidence rate" of these symptoms are "likely higher" with both vaccines—which means that more women have likely experienced this side effect and didn't notice or didn't report it.

As a result, the SBI issued this recommendation: "If possible, and when it does not unduly delay care, consider scheduling screening exams prior to the first dose of a COVID-19 vaccination or 4-6 weeks following the second dose of a COVID-19 vaccination." The SBI also recommends that clinicians find out a patient's vaccination status before their mammogram and when the vaccine was given.

The main concern: A vaccinated woman may worry that she's developed breast cancer after spotting a breast lump or receive a false reading on her mammogram and be subject to unnecessary tests.

While the news is a little freaky, doctors aren't shocked that this is happening. Here's why.

First, a recap on how your lymph system works

Your body has a network of lymph vessels and lymph nodes that's part of your immune system. The lymph system collects fluid, waste material, and other things like viruses and bacteria that are in your tissues outside of your bloodstream, the American Cancer Society (ACS) explains.

The lymph vessels are similar to your blood vessels, but carry a clear, watery fluid called lymph instead of blood. Lymph fluid can do a few different things, but one important function is its ability to fight infections through the use of white blood cells that it carries. Your lymph nodes are small structures that work as filters for harmful substances, and they contain immune cells that help you fight infections, the ACS says.

When you have an infection, injury, or cancer, the node in that area may swell or enlarge as it tries to filter out the bad cells. And, while lymph node swelling is usually a sign of an infection, it can also signal cancer in that area, the ACS says.

Here are the 'official' side effects of the COVID-19 vaccine

The CDC lists the following as potential side effects of receiving either the Moderna or Pfizer COVID-19 vaccine:

  • Pain in the arm where you received the shot
  • Swelling in the arm where you received the shot
  • Fever
  • Chills
  • Tiredness
  • Headache

OK, so why might the COVID-19 vaccine mimic breast cancer symptoms?

It's all part of your immune system's reaction to the vaccine, William Schaffner, MD, an infectious disease specialist and professor at the Vanderbilt University School of Medicine, tells Health. "The lymph nodes are part of your immune system and, although you are inoculated in your outer arm, some of that material can get into your local lymph nodes," he explains. "They can be activated as part of the response of the immune system." Cue the tenderness and swelling.

This can happen with certain vaccines and infections, infectious disease expert Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security, tells Health. "Any type of immune stimulation will eventually impact the lymph nodes near the site of infection or injection," he says.

Discomfort—and potential freakout—aside, Dr. Schaffner says the swelling isn't necessarily a bad thing: "It's another bit of evidence that your immune system is being awakened and is responding to the vaccine."

How long will this symptom last, and what should you do if you experience it after getting vaccinated?

It's not entirely clear, but Dr. Adalja says the lymph node swelling and tenderness can stick around for a while. "It will usually last for a week or so," he says, adding that it could take longer. That's why Dr. Schaffner says the recommendation to wait four weeks after your vaccine to have a mammogram is "good advice."

While a lump or swelling near your breast can be linked to the COVID-19 vaccine it can also be a sign of another infection or even breast cancer. Dr. Schaffner recommends calling your doctor if you notice this symptom and it doesn't go away within a week or if it feels like the discomfort is getting worse. And, Dr. Adalja says, if you had the bump before you were vaccinated, definitely get it checked out.

But, if you have a lump or swelling, the pain is manageable, and you're pretty certain it's due to the COVID-19 vaccine, Dr. Adalja says you can try to apply cool compresses to the area to try to get relief.

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDCWHO, and their local public health department as resources.

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