What Causes Armpit Pain After COVID Vaccine in Some People?

As an increasing number of people globally receive COVID vaccinations unusual side effects have come to light, including underarm pain as a result of swollen lymph nodes.

Many of us are aware of the more common side effects of COVID vaccinations, like fatigue and a sore arm, but swollen lymph nodes under the arm caught the attention of doctors as they can be a symptom of other conditions like breast cancer or leukemia.

Yale Medicine says that these side effects are normal and harmless, pointing out that medical experts want to get the word out about this to avoid alarm in those who experience lymph node swelling and other less common side effects.

Dr. Brita Roy, an internal medicine physician and director of population health for Yale Medicine, said: "As more people get vaccinated, it's important to allay fears and avoid unnecessary testing or treatment for conditions that should quickly resolve."

Swollen lymph nodes are a side effect of the Moderna and Pfizer-BioNTech vaccines that arise as a result of the messenger RNA (mRNA) technology they use. That means that this side effect isn't commonly seen with the Johnson & Johnson vaccine.

The swelling tends to occur a few days after the vaccine is administered in the lymph nodes in the armpit or near the collarbone of the person who received it. They can feel like little lumps and can be tender, but usually fade away after a period of around 10 days. Many people won't notice the swelling in their lymph nodes at all.

Roy said: "The COVID-19 vaccination is given in the arm and the closest lymph nodes are the ones under your arm, so that is where the reaction is occurring.

"It's completely normal. It's your immune system reacting to the vaccine, as it should."

The Cleveland Clinic pointed out that because lymph nodes are part of the immune system that vaccines seek to stimulate, swelling is a possible side effect of any vaccine, but this has been more prominent with COVID mRNA vaccines.

Diagnostic radiologist Dr. Laura Dean told the clinic that even though swollen lymph nodes can be a symptom of cancer they can also result from other, often less serious, conditions like arthritis, autoimmune conditions, colds and flu, sinus infections and strep throat.

Adapting Cancer Screening

She added that cancer screening questions are being adapted to include inquiries about vaccination status as well as considering the patient's history of these conditions.

One of the issues with lymph node swelling caused by COVID vaccines is that it seems to occur in the same areas affected by breast cancer. Dean said: "If breast cancer moves outside of the breasts, it tends to go to those patterns of the lymph fluid inside the breast tissue."

According to Yale Medicine, because enlarged lymph nodes can appear on imaging scans such as mammograms, CT scans, MRIs and ultrasounds, the side effect has raised concern among those unfamiliar with it. Because of the similarity to signs of breast cancer, this has been the case for some women having mammograms.

Roy said: "It's challenging right now as, here in Connecticut, we are vaccinating in the age bracket in which every woman who is currently eligible for the COVID vaccine should be getting a yearly mammogram."

She says that the challenge for doctors and patients is to book a mammogram at least a month after vaccination, but with delaying a routine screening.

Roy concluded: "At Yale, we have been talking to our breast radiologists and the national radiology associations. Ideally, you would not have a mammogram scheduled within a month of receiving your last dose of an mRNA vaccine.

"However, if schedules are full, postponing it might mean having to go a very long time. So, if it's possible to have your mammogram done before you are vaccinated, that's ideal."

Roy also said that anyone who can still feel that their lymph nodes are swollen a few weeks after their vaccination should seek medical advice.

COVID Under Arm
A file photo of a woman examining her underarm and an illustration of a COVID vaccination dose being drawn. People experiencing swollen lymph nodes and armpit pain after a COVID shot shouldn't be concerned, experts say. triocean/ solarseven/Getty