Can a Recent COVID-19 Vaccine Affect Your Mammogram Results?

The short answer: Yes. A COVID-19 vaccine can make the lymph nodes in the armpit on the injected side swell, and a mammogram can show that swelling. It is a normal immune response and is almost always harmless. The Society of Breast Imaging (SBI) no longer recommends delaying a screening mammogram around a COVID-19 vaccination. Keep your appointment, and tell the technologist the date of your shot and which arm it went in.

Why does a COVID-19 vaccine show up on a mammogram?

A vaccine in the upper arm drains to the lymph nodes in the armpit on that side. The nodes get larger while the body makes antibodies. A mammogram includes part of the armpit, so the radiologist can see enlarged nodes there. The medical term is axillary adenopathy or axillary lymphadenopathy.

Radiologists look closely at this finding because breast cancer can also spread to the armpit nodes. Before the vaccines, the finding was rare. The SBI statement gives a baseline of 0.02% to 0.04% of screening mammograms.

How often do swollen lymph nodes show up after the vaccine?

The answer depends on who is looking. People notice swelling much less often than imaging finds it.

• Moderna trial, felt by the participant: CDC's summary of the trial data reports armpit swelling or tenderness after dose 2 in 16.0% of vaccine recipients aged 18 to 64, against 4.3% with placebo. In people 65 and older the figures were 8.4% and 2.5%.
• Pfizer-BioNTech trial, reported as an adverse event: CDC's summary lists 64 cases of lymphadenopathy in the vaccine group and 6 in the placebo group among adults.
• Seen on breast imaging: A Stanford study of 3,008 women vaccinated in the previous 6 weeks found swollen nodes on the vaccinated side in 308 women (10%). The rate was 8% on screening mammograms and 27% on breast MRI.
• Vaccinated against unvaccinated: A Baylor study of 1,027 screening mammograms found swollen nodes in 13.2% of women who had the Pfizer-BioNTech vaccine, 9.5% who had Moderna, and 1.2% of women who were not vaccinated.

The SBI statement cites a range of 2.4% to 35% across radiology studies. MRI and ultrasound find more swollen nodes than a mammogram does. mri.md explains breast MRI in plain language.

How long does the swelling last?

Swelling that you can feel is usually brief. In the Pfizer-BioNTech trial it started 2 to 4 days after the shot and lasted about 10 days on average. In the Moderna trial the median duration of reported lymphadenopathy was 1 to 2 days.

Swelling that only imaging can see lasts much longer. This fact changed the advice on scheduling.

• A Weill Cornell study followed 111 women with ultrasound until the nodes returned to normal. Resolution took a mean of 127 days after the first vaccine dose.
• The same group studied 54 women after a booster dose. Resolution took a mean of 102 days after the booster.
• The SBI statement says swollen nodes have appeared as early as 1 day and as late as 71 days after vaccination. It adds that swelling may persist for up to 43 weeks.

Should I reschedule my mammogram around my vaccine?

No. The current SBI position is to keep the appointment.

The advice did change. In early 2021 the SBI suggested that women consider a screening mammogram before the first dose, or 4 to 6 weeks after the second dose.

In February 2022 the SBI revised its recommendations. The revised statement says the society "no longer recommends delaying screening mammograms around COVID-19 vaccinations." It gives two reasons. The swelling can last far longer than 6 weeks, so a short delay does not avoid it. Screening had also fallen during the pandemic, and the society said more delays should be avoided. The February 2022 revision is still the document on the SBI position statements page as of October 2026.

European guidance moved the same way. The European Society of Breast Imaging said in its 2023 revision that breast exams should not be delayed or rescheduled because of COVID-19 vaccination.

The SBI recommendations apply to women with no symptoms, average risk, and no history of breast cancer or another cancer that can involve the armpit nodes. If you have a breast cancer history, ask your care team which arm to use for the shot. One published approach from Massachusetts General Hospital advises the opposite arm or the thigh for patients with a recent breast cancer diagnosis.

What happens if the radiologist finds a swollen node?

It depends on your history and on what else the images show.

• Benign reading, no extra tests. The revised SBI statement says a benign assessment (BI-RADS category 2) may be appropriate. This applies when the swelling is on one side, the vaccine went in that arm recently, and the mammogram shows nothing else suspicious. Our guide to BI-RADS categories explains the scores.
• Callback. Some centers still ask you to return, usually for an ultrasound of the armpit. This is more likely if nobody recorded your vaccine details, or if you have a cancer history. See what a mammogram callback means.
• Short-interval follow-up. If the radiologist wants to confirm that the node shrinks, the SBI recommends a follow-up interval of 12 weeks or more (BI-RADS category 3). The earlier advice was 4 to 12 weeks.
• Biopsy. The SBI says to consider lymph node sampling if the node has grown at follow-up. A node that is smaller but still present can be called benign or checked again at six months.

Outcomes are reassuring. In the Stanford study, 259 of the 308 women (84%) needed no follow-up imaging. Thirteen women had a biopsy, and every biopsy was benign.

The vaccine is not always the cause. A Radiology review describes a 60-year-old woman with swollen nodes and a suspicious breast finding 9 weeks after vaccination. Her biopsy showed breast cancer that had spread to the nodes. A swollen node together with a suspicious breast finding gets a full workup at once.

What should I tell the technologist?

The SBI asks imaging centers to collect COVID-19 vaccination status on the intake form, including the date and the side. Give this information even if nobody asks.

1. The date of your most recent COVID-19 vaccine or booster.
2. Which arm it went in, left or right.
3. Any other vaccine you had in the last few months, with the date and the arm.
4. Any lump, swelling, or tenderness you can feel in the armpit, and when it started.
5. Any personal history of breast cancer, lymphoma, or melanoma.

The rest of the visit does not change. See what to expect at a mammogram.

If an armpit lump lasts more than a few weeks, grows, or appears on the side opposite your shot, tell your clinician. symptom.md covers how to sort symptoms that need a visit.

Can flu or other vaccines do the same thing?

Yes, but the evidence is thinner. The SBI intake wording states that "vaccines of all types can result in temporary swelling of the lymph nodes." A 2025 radiology review says lymph node swelling is also known after the seasonal influenza vaccine. The same review says systematic studies of other vaccines are missing.

The SBI recommendations address COVID-19 vaccines only. The practical step is the same for any vaccine: report it, with the date and the arm.

The bottom line

A recent COVID-19 vaccine can cause swollen armpit lymph nodes that appear on a mammogram. Imaging studies found them in about 1 in 10 recently vaccinated women, and they can stay visible for 3 to 4 months or longer. Since February 2022 the Society of Breast Imaging has advised women not to delay screening because of a vaccine. Tell the technologist your vaccine date and arm. If a swollen node needs a second look, the usual step is an ultrasound 12 weeks or more later.

Last updated: October 2026. This article is for informational purposes only and does not constitute medical advice. Talk to your doctor or breast imaging center about your own screening schedule, vaccine timing, and any lump you can feel.