Armpit pain is a common side effect from mRNA COVID-19 vaccines

Armpits contain lymph nodes, and swollen lymph nodes are a sign that an mRNA COVID-19 vaccine is working.

The pain may be bothersome, but it usually goes away on its own and doesn’t usually require medical attention.

The pain was noticed during trials of both the Moderna and Pfizer vaccines.

What’s going on with sore armpits after the COVID-19 vaccine?

11.6% of people in the Moderna trial suffered this side effect after the first dose. 16% suffered the side effect after their second dose. With Pfizer, only .3% reported soreness in the armpit.

Related: What are the side effects to the COVID-19 booster shot?


This is caused by swelling of lymph nodes in that general area.

The lymph nodes are part of the immune system, and the ones in the armpit are located closest to the injection site.

The lymph nodes swelling is in reaction to the vaccine, signaling the immune system to stimulate.

The boosters work the same way, but the Moderna booster is a half dose.

Gerald Harmon, the American Medical Association’s President, stated that the adverse events following a vaccine are shown to be the same as or less severe with a booster shot.

Related: What are the COVID-19 vaccine side effects for children?


To help minimize the pain caused by swelling lymph nodes in the armpit, make sure to get lots of rest, drink fluids, and take an OTC medication like ibuprofen.

If you need a mammogram, it’s best to schedule it at least one month after getting the vaccine. Swollen lymph nodes can look like early signs of breast cancer.

In the event that postponing the appointment would make the wait too long, then it’s better to just go ahead with it but inform your doctor of the recent vaccine.

If the side effect appears to be worsening or does not go away within a few days, it’s suggested you contact your physician.


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