Don’t panic if you get swollen lymph nodes after a vaccine booster. But be aware if you’re due for a mammogram, doctors say

By Holly Yan, CNN

Some people who recently got a booster dose of COVID-19 vaccine are noticing swollen lymph nodes.

Don’t panic, doctors say. Swollen lymph nodes caused by vaccination are temporary, harmless and a sign that the vaccine is working.

But to avoid unnecessary anxiety and uncertainty, women planning to get a mammogram should know that swollen lymph nodes right after a vaccine dose might show up on a mammogram, the US Food and Drug Administration’s top vaccine official said this week.

“If you are a woman, and you’re going to get a mammogram, and you get your booster shot, call and tell them you’re getting it (or) you’ve gotten it,” Dr. Peter Marks, head of the FDA’s Center for Biologics Evaluation and Research, said at a town hall hosted by the COVID-19 Vaccine Education and Equity Project.

“If you’re going to get it, you might want to get your mammogram first before you get it, or you might want to wait a couple of weeks because if those lymph nodes turn up on a mammogram, they may trigger a false, further investigation,” Marks said. “It’s really a harmless thing, except if it triggers extra medical investigation, so that’s just something to be aware of.”

To be clear: “The COVID vaccine does not cause breast cancer or increase your risk for breast cancer,” said Dr. Lisa Ann Mullen, breast imaging fellowship director and assistant professor of radiology and radiological science at Johns Hopkins Medicine. “But it can make the lymph nodes larger, and that includes (after) the booster.”

Why does this happen?

After a vaccine shot to the arm, lymph nodes in the armpit area can sometimes swell as the immune system is activated and builds an army of antibodies.

And those swollen lymph nodes might show up on mammograms, said Dr. Connie Lehman, chief of breast imaging at Massachusetts General Hospital and a professor of radiology at Harvard Medical School.

“We’re not surprised at all. This is an extremely effective vaccine,” Lehman told CNN on Thursday.

“It incites an immune response by the body that is necessary to fight off the COVID-19 virus, should it enter a person’s body,” Lehman said. “So these enlarged lymph nodes are evidence that the vaccine is doing exactly what our bodies need it to do.”

It’s not just COVID-19 vaccines — the flu shot, the shingles vaccine and the diphtheria/tetanus/pertussis (D-TaP) shot can also temporarily change the appearance of lymph nodes, Mullen said.

She often sees enlarged lymph nodes from the flu vaccine show up on mammograms in October.

“I wish we could move Breast Cancer Awareness Month from October to some other month, like May or June, because every year it has been flu vaccine season as well,” Mullen told CNN on Thursday. “I call back some people from screening, who I know they had a flu vaccine, and their lymph nodes are a little big.”

“And you know it’s probably because of the flu vaccine, but I can’t be 100% sure. So often we’ll ask those women to come in,” possibly for an ultrasound to investigate further, Mullen said.

So when should women coordinate vaccines and mammograms?

Women eligible for an additional dose of vaccine who also have a mammogram planned for the near future should check with their healthcare provider, said Marks, the FDA vaccine official.

Not all doctors will agree, and not all patients will have the same circumstances, Mullen said.

She said it’s important to get vaccine doses on schedule. And if your regularly scheduled mammogram is several weeks away, any vaccine-induced swollen lymph nodes probably wouldn’t be an issue, Mullen said.

If you’re due for a mammogram soon, Mullen suggests getting it. She said results are typically available within a few days, and women can get vaccinated afterward — reducing the chances of vaccine-induced swollen lymph nodes showing up on a mammogram.

But if a woman recently got vaccinated and has swollen lymph nodes, she may want to wait a few weeks before getting a mammogram, Mullen said.

“If it’s possible to do a mammogram before the COVID vaccine series, or before the booster, then that’s great. If it’s not possible, and you can wait several weeks (for a mammogram), that’s OK, too,” she said.

There’s one circumstance in which women should get examined for breast cancer immediately — regardless if they just got a shot, Mullen said.

“If this is a diagnostic situation — and by that I mean somebody has a symptom in their breast like they have a nipple discharge, they have breast pain, there’s something going on in the breast that’s different and new for them, or their doctor feels a lump … we want them to come right away,” she said.

“I don’t care whether they had their vaccine yesterday. Just come on in, and we’ll work on whatever the problem is,” Mullen said.

‘Don’t delay either. Get both’

Lehman said it’s important not to skip or delay mammograms — something many women have already done during the pandemic.

She encourages women to get screened for breast cancer as scheduled — even if they recently got vaccinated.

“Don’t delay either. Get both,” Lehman said. She said there are ways to help detect whether a swollen lymph node is simply the result of vaccination or something more concerning.

“There’s a very specific list we check through,” Lehman said.

“We document every single patient where their COVID vaccine was. So I see a mammogram come up, and the woman had a vaccine in her right arm, and she has asymmetrically enlarged lymph nodes in the right armpit, I put a statement in to the patient and her doctor and I say, ‘This is a normal response to the vaccine. If you have any clinical concerns, if you can feel the swelling, it gets worse, if you have any concerns, see your doctor. You can always do more evaluation,'” she said.

“Please don’t delay your mammogram, and please don’t delay your vaccination.”

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CNN’s Virginia Langmaid and Sandee LaMotte contributed to this report.