Many people have fears surrounding the new COVID-19 vaccines, some of which are due to medical misinformation. Some are concerned about rumored reactions to the vaccines, such as arm soreness, fever, chills, nausea, and feeling rundown. It is true that some patients experience these reactions which are signs of the immune system reacting to the vaccine and making antibodies so that the body is ready to fight if it encounters the actual virus.
There has been recent buzz surrounding another reaction to the vaccine: temporary swollen and tender lymph nodes within the underarm on the same side of the body that the vaccine was given. This is also an appropriate response that has been seen commonly with other older vaccines. Lymph nodes are a normal part of human anatomy and can be found throughout the body. They are part of our immune system and act as a filter for many things found in the body, such as infection and even cancer. Lymph nodes can enlarge and sometimes become tender when they are reacting to cancer. In particular, lymph nodes in the underarm can enlarge when filtering breast cancer.
Swollen and tender lymph nodes in reaction to the COVID vaccines is temporary and usually lasts for up to 2-3 weeks. This is important because if a woman has a screening mammogram while the lymph nodes are still swollen, the nodes can sometimes be seen on the mammogram which can mimic signs of breast cancer. The Society of Breast Imaging now recommends that women schedule their screening mammograms 4-6 weeks after their final COVID vaccination dose since enlarged lymph nodes related to the vaccine will have usually returned to normal size by that time.
Vaccine or not, it is always important to remember that whenever a new lump is found within the underarm or breast, both women and men should inform their healthcare providers, so that appropriate testing (most commonly a diagnostic mammogram and/or ultrasound) can be performed.