September 16, 2021

Swollen Lymph Nodes After COVID-19 Vaccine: Why You Shouldn’t Be Alarmed

Our expert explains why swollen lymph nodes happen

covid vaccine swollen lymph nodes

As more people across the globe continue to receive the COVID-19 vaccine, we’ve learned quite a bit about the side effects that the vaccine can cause.


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But one side effect — swollen lymph nodes under your arms — has been getting more notice because it’s an overlapping symptom for other issues. It’s important to know what’s a side effect of the vaccine and what’s a sign of something that needs further attention.

To better understand what’s causing this symptom and what you should know before getting your COVID-19 vaccine, we talked to diagnostic radiologist Laura Dean, MD.

What are the COVID-19 vaccine side effects?

The most common side effects of the COVID-19 vaccine include:

  • Fever.
  • Chills.
  • Muscle aches.
  • General fatigue.
  • Headaches.
  • Soreness at point of injection (also known as “COVID arm”).

The side effects are typically mild, last between 24-48 hours and are most commonly felt after the second dose of the mRNA vaccines (Pfizer and Moderna) or the single Johnson & Johnson dose.

Why does the COVID-19 vaccine cause lymph nodes to swell?

Lymph nodes are part of the body’s immune system so, according to Dr. Dean, swollen lymph nodes are a potential side effect of any vaccine. “The whole point of the vaccine is to get your immune system to mount a response to whatever the vaccine agent is,” she says.

But it seems that the COVID-19 vaccines can cause a more robust swelling in lymph nodes. And those swollen lymph nodes, like other side effects, vary from person to person. “We’re still learning about these vaccines and the side effects as more and more people receive them,” Dr. Dean says.

The swollen lymph nodes generally appear a few days after someone receives the vaccine, on the same side of the body as they got the shot. “We’re still watching these examples, but right now we think that symptom subsides with a few days to a few weeks,” she adds.

What do swollen lymph nodes usually mean?

Swollen lymph nodes can sometimes be a symptom of cancer. But it’s important to remember that they can have a number of other causes. And while the COVID-19 vaccine appears to only cause swelling on one side, swelling in lymph nodes on both sides of the body is also not necessarily a sign of cancer.


“You see general lymph node enlargement — under the arms, in the chest or groin — with something like lymphoma,” says Dr. Dean. “But there are other reasons you’d see that, too, which are far less serious than cancer.”

Other causes of swollen lymph nodes include:

There are additional conditions, too, that Dr. Dean says healthcare providers may look into. “We address the issue by taking a very detailed patient history and looking for other conditions that may cause the swelling like rheumatoid arthritis, lupus or autoimmune diseases.”

And, yes, this includes swelling on just one side. “We don’t want to miss something because a lymph node on just one side is swollen,” she adds. “But we’ve also added questions about recent COVID-19 vaccines to our screening questions to make sure we’re getting a full view of what might be affecting the patient.”

Still, if you’re concerned by the appearance of swollen lymph nodes within a day or two after receiving your COVID-19 vaccine, it’s worth contacting your healthcare provider. With their knowledge of your medical history, they have the necessary context to make a full evaluation.

Swollen lymph nodes as a sign of breast cancer

It’s the location of the lymph nodes involved with this particular side effect that’s causing concern. Many times (but not always) the location of a person’s lymph node swelling corresponds to the site of infection. For many who have breast cancer, that includes the lymph nodes in the armpits.

“If breast cancer moves outside of the breasts, it tends to go to those patterns of the lymph fluid inside the breast tissue,” Dr. Dean explains. “It’s a very integrated system, so it’s one of the areas we closely scrutinize.”

Because early detection is so key to treating breast cancer, it’s understandable that this overlapping symptom is causing a little bit of confusion and even alarm in many patients.


Does this affect my preventive care plan?

The most important thing, Dr. Dean says, is that patients maintain their preventive care plan for breast cancer, especially mammogram screenings.

The Society of Breast Imaging recommends scheduling your mammogram either before your first dose of the COVID-19 vaccine or about four to six weeks following your second dose, if possible. If that’s not possible, though, it’s important to keep both your scheduled screening and your vaccine appointment.

“We’ll work with you to explain what’s going on, what we see and what might be a side effect,” Dr. Dean adds. “And if there’s potential overlap, you can schedule a short-term follow-up screening for a few weeks later just to be safe.”

The bottom line: get vaccinated

Again, Dr. Dean stresses that there’s no reason to be alarmed about getting swollen lymph nodes from the COVID-19 vaccine. “This type of reactive change that we’re seeing with the COVID-19 vaccine is exactly what we should see,” she says. “It’s your body mounting the immune response as it’s supposed.

While those enlarged lymph nodes may be worrisome, she adds that healthcare providers are aware and monitoring them in patients. “We’re keeping an eye on this side effect and when it comes to your mammogram screening, we’re ready to explore any abnormalities in that context.”

Finally, she reiterates how important it is to maintain your preventative care appointments despite these side effects. “It’s extremely important COVID-19 vaccinations continue. And it’s also important to know that we’ll never turn any patient away from a mammogram screening for getting their vaccination. We’re armed with as much information as possible and we’ll work with every patient to make sure they get the care they need.”

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