There are side effects to the COVID-19 vaccines, but experts say the benefits greatly outweigh the risks. “I would take whatever vaccine would be available to me as quickly as possible,” Dr. Anthony Fauci, the nation’s top infectious disease expert, said recently. “We want to get as many people vaccinated as quickly and expeditiously as possible.”

But one such side effect is leading to a potentially frightening cancer scare – leading doctors to warn patients not to panic.

According to the CDC, possible reactions to COVID-19 shots can include pain at the injection site, fever, fatigue, and swollen lymph nodes.

Breast imaging centers have started to see more patients with enlarged lymph nodes, which are part of the immune system, helping to store and release white blood cells and clearing away waste. 

Sometimes swollen lymph nodes, specifically under the armpit, swell after vaccinations, but could be mistaken for cancer if it shows up on a scan, like  a mammogram. Lumps under armpit skin could be a sign of cancer, but are usually not if they appear shortly after receiving the COVID-19 vaccine.

Dr. Sarah Cate, who heads the Special Surveillance and Breast Program at Mount Sinai Medical Center, says they’ve had to change the way they operate since the COVID-19 vaccine distribution went into full swing.

“Within my own practice we've had several patients that have come for their mammogram or ultrasound that have recently been vaccinated for COVID-19,” Dr. Cate told Spectrum News. “And what's showing up on the imaging is that the lymph nodes on the same side that they got the vaccine in the armpit are enlarged.”

“We are coming up with a system to identify those patients prior to coming in for the imaging,” Dr. Cate added, “because obviously it creates a lot of anxiety for those patients to get an abnormal imaging result.”

Cate is now following recommendations from the Society of Breast Imaging, which issued guidelines for mammograms after receiving a COVID-19 vaccination. 

For women who still show up for their scheduled mammogram shortly after being vaccinated, experts recommend they return for follow-up imaging 4 to 12 weeks later to avoid the typical cascade of testing and limit cancer scares. 

Dr. Cate says there is also concern that women will continue to put off or forget about their mammogram appointments completely, which has been a concerning trend during the COVID-19 pandemic – according to the Epic Health Research Center, screenings for breast and cervical cancers dropped by 94%, with colon cancer screenings down 86%, from January through April of 2020.

“I think we're already seeing the repercussions of people not going for screening from last spring, so more patients are coming in that are diagnosed at later stages, more patients are coming in that need chemotherapy before the surgery. More patients are being diagnosed as metastatic, which means the cancer spread outside the breast in the armpit,” said Cate. “I really can't reinforce enough that the sooner you get the mammogram, the sooner you get diagnosed, the less likely you are to need more treatment and more drastic treatment.”

Dr. Cate urges women not to make the decision whether to delay a mammogram appointment in favor of getting vaccinated. 

“If you have any concern about the timing of the mammogram and relationship to the vaccine, and if you can't decide if you have lymph nodes that are enlarged, call your doctor,” Dr. Cate said, “so that decision can be made with good sound medical advice behind it.”

A lightly edited transcript of Erin Billups’ conversation with Dr. Sarah Cate:

Q: Why is the vaccine having this impact on the lymph nodes?

A: Most patients are getting vaccinated in their deltoid. And the lymph nodes that drain that area, meaning the upper arm, are located in the arm after the axilla [a.k.a. the underarm]. So actually, having some lymph nodes that enlarged show that you're mounting an immune response to the vaccine. So, it's actually a good sign. But the question is when it interferes with breast imaging and raises that question of a false positive, that's not a good side effect of the vaccine.

Q. That was my next question; in the past, pre-COVID-19, when someone would come in for a mammogram and have an inflamed lymph node, what would that indicate?

A. Enlarged lymph nodes and inflamed lymph node can be anything from the benign reasons; sometimes even hair removal can cause an inflamed lymph node underneath the armpit. But the most concerning sign of an enlarged lymph node is that it's breast cancer that spread to the lymph nodes underneath the armpit on that side, or that it's a breast cancer that started in the lymph nodes or that it's a lymphoma. So, we have to rule that out. And prior to the current vaccine, really, anyone with an enlarged lymph node was treated as if they had a cancer until we got the answer that they did not.

Q. If you have had a mammogram scheduled around the time of a vaccine, which one should you do first, which is more important at this point?

A. There were a lot of delays in screening mammography due to COVID-19. So, we really don't want to tell patients not to get a mammogram, especially if they missed one in 2020. But especially for patients that can feel lymph nodes right after the vaccine, I would say push the mammogram for about three weeks, just delay it or call your doctor and say, ‘what is the concern here? Is this just a screening mammogram that I'm going for because I'm 41,’ or was it something that your doctor felt and wanted to get worked up more quickly?

Q. If it’s just a reaction to the vaccine, what should it feel like?

A. Lymph nodes that are what we call reactive, which means that they're caused by something that's external to the body and they're benign, which means they're not part of the cancer process and they'll go away. They are usually very mobile, they're usually very soft, they're usually very squishy. Cancer lymph nodes are more likely to be multiple, they're more likely to be firm or hard. They're less likely to be painful and they're less likely to slowly shrink over the course of a few days.

Q. Some might feel like putting off that mammogram appointment may not be such a big deal for a year or so because cancers usually grow slowly.

A. Yes, the garden variety of breast cancer is usually a slow growing, slow dividing type of cell, but there are some subtypes of breast cancer that are more aggressive that will spread more quickly. The problem is that you really don't know how a cancer will behave. A lot of times in younger patients, cancers that should be more indolent will be more aggressive. We see this a lot in pregnancy associated breast cancers where a regular, slow growing, breast cancer can get supercharged because of the hormones. The question is, obviously, had we diagnosed it last year, what would the stage difference be? And we don't have that data yet, but we're certainly seeing a lot of later stage cancers already.