Could the COVID Vaccine Affect Mammogram Results?

One vaccine side effect is creating some confusion in breast cancer screening appointments.

by Sarah Ellis Health Writer

Mammograms are an essential health care screening tool for women. The American Cancer Society recommends that women ages 45 to 54 get them every year, with the choice to start earlier (between 40-44) encouraged. These screenings can also be a source of anxiety, especially for women personally affected by breast cancer—either as a loved one or as a survivor herself.

So, if you’ve seen the recent reports suggesting the COVID vaccine might alter mammogram results, your first reaction is probably, “Umm, what?! Do I need to be concerned about this?”

Before you freak out, let us catch you up to speed: On January 22, the Society of Breast Imaging (SBI) released a report outlining the prevalence of lymph node swelling (adenopathy, as it is officially called) after COVID vaccination. Of people receiving the Moderna vaccine, 11.6% reported swelling in the lymph nodes after the first shot, and 16% reported the occurrence after the second shot. Pfizer reported fewer incidences of lymph node swelling—only 64 adenopathy cases in their entire clinical trial population—but SBI estimates that the actual number of people who experience post-vaccination lymph node swelling is likely higher than reported.

You can’t always feel lymph node swelling, but sometimes you may notice a soft lump and some tenderness in your underarm area. The swelling can show up on imaging tests like mammograms and MRIs, causing some initial confusion about the results. “Being in a pandemic, this makes everybody a little bit more anxious,” says Tari King, M.D., chief of breast surgery at Dana-Farber/Brigham and Women's Cancer Center in Boston. But please know that this does not have to result in a breast cancer scare. Here’s what to be aware of before you go in for screening.

Lymph Node Swelling After the COVID Vaccine

Your lymph nodes are part of your body’s immune system—they help to filter harmful substances and ward off infections. They can be found all over your body, but we’re specifically looking at underarm lymph nodes here, which are located underneath the skin where the hair grows.

When you get a vaccine, your lymph nodes sometimes swell up in reaction to the foreign invader. You might notice a lump under your arm a few days after vaccination, which will persist anywhere from two days to several weeks. “Lymph nodes are the body’s germ-fighting immune system, and their being enlarged after a vaccine is your way of responding,” says Sandhya Pruthi, M.D., professor of medicine at Mayo Clinic in Rochester, MN. “The body is saying, ‘We’re going to build up the defense to fight against this virus.’”

Sounds like a good thing, right? It is, and it’s also totally normal. “Vaccinations causing swelling of the lymph nodes is not unique to the COVID vaccine,” Dr. King says. This also happens with the flu vaccine, though usually to a lesser extent.

Mammograms and the COVID Vaccine

If you get a breast screening in the weeks after your COVID vaccination, the radiologist might notice swelling in your underarm area. Typically, this is a sign that something isn’t quite right. “It can create some confusion or uncertainty around the results of a mammogram if the breast imager is not aware that the patient has had a recent vaccine,” Dr. King says. The best way to counter this is simply to tell your provider that you’ve recently had the COVID shot and which arm you had it in.

Dr. Pruthi explains: “If somebody has lymph node swelling but the mammogram is [otherwise] normal, and the patient says, ‘I just had my COVID vaccine last week,’ we can put two and two together and say, ‘This is your lymph nodes swelling from your COVID vaccine, and it’s nothing to worry about.’” Having that context is essential for the radiologist to identify the reason for the underarm swelling.

Breast cancer survivors can even take the proactive step of asking for their COVID vaccine in the opposite arm from their affected breast, Dr. King suggests. Bilateral breast cancer survivors can ask to receive the vaccine in their thigh instead of their arm (only if you want—totally not required). This will avoid any chance of adenopathy causing a suspicious mammogram reading in that previously affected area. “The most important thing is communicating that you’ve had a recent vaccine and where you’ve had it when you present for any type of imaging within six weeks of vaccination,” Dr. King says. This clears up any potential alarm from the outset.

Should I Reschedule My Breast Cancer Screening After Vaccination?

To avoid confusion, you may be tempted to put off your screening mammogram until a few months after your second vaccine dose. The American Cancer Society does not recommend postponing your mammogram without talking to your doctor first. “We already had a lot of women miss their screening mammograms during the early phases of the pandemic, when screening was shut down for a while,” Dr. King recalls. “We certainly don’t want to cause any other delays in women getting back in for their screenings.”

If you’re really committed to changing your appointment date, Dr. Pruthi says that routine screening mammograms can usually be postponed a month or so. “You’ll be fine—you are still within your one-year follow-up,” she notes. SRI recommends that patients consider scheduling their screenings before the first COVID vaccine dose or four to six weeks following the second dose. But this should only be done after talking to your doctor, and only if you have no concerning symptoms to report. “If you feel a lump in your breast, that takes precedent,” Dr. Pruthi says. “Let the radiologist do the appropriate diagnostic work”—even if that means coming in right after your COVID vaccine.

More on Lymph Node Swelling as a Vaccine Side Effect

There are a few other points worth making here. First, there is no evidence to suggest that COVID-19 itself causes swelling of the lymph nodes. That hasn’t been reported as a notable side effect of the virus. “The stimulating of the immune system from the vaccine is the cause of the lymph nodes being swollen,” Dr. King explains. So, if you haven’t been vaccinated and you notice swelling in your underarm area, don’t write it off as a symptom of COVID. Report it to your doctor to get their advice on whether you should be screened.

For lymph node swelling after vaccination, this should go down within six weeks of your second dose of the COVID shot. “If the swollen lymph nodes persist beyond six weeks, that’s when we’re recommending for women to return for additional follow-up and recommendations,” Dr. King says. Your doctor will likely want to do a reassessment of the swollen area to make sure there is nothing else going on. But don’t worry—in most cases, post-vaccine adenopathy will go away long before this. SRI reports that most incidents went away after ten days or less.

Knowledge is power here, and it can help make this situation a lot less frightening. “The finding of an enlarged lymph node creates a lot of anxiety,” Dr. King says, “so we want to make sure that we know when patients have had a recent vaccination so we don’t contribute to that anxiety by recommending unnecessary testing.” Your provider can answer any specific questions you have; don’t be afraid to go to them for help if you need it.

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Sarah Ellis
Meet Our Writer
Sarah Ellis

Sarah Ellis is a wellness and culture writer who covers everything from contraceptive access to chronic health conditions to fitness trends. She is originally from Nashville, Tennessee and currently resides in NYC. She has written for Elite Daily, Greatist, mindbodygreen and others. When she’s not writing, Sarah loves distance running, vegan food, and getting the most out of her library card.