Swollen lymph nodes and lumps under the armpit, doctors say, are a side effect of the COVID-19 vaccine."The job of the lymph node is to actually have the response to the vaccine and create antibodies that will protect us, if we got the virus," said Allegheny Health Network Dr. Robin Sobolewski. "Their job is to enlarge and work overtime so that's a normal response."Pam Lynn never experienced swollen lymph nodes, but she said her mammogram, four days after her second dose of the vaccine, showed an abnormality."I get a phone call saying there were some abnormalities, which is scary, and it's on your left side and I actually had a history of breast cancer on that side, so I was doubly unsettled," said Lynn.Lynn said she waited weeks for a sonogram, where doctors realized that swelling found on the images, was the result of the vaccine. The Society of Breast Imaging is warning that this side effect could mimic symptoms of breast cancer and they are recommending that screening exams are either scheduled before the first dose of the vaccine, or 4-6 weeks after the second, in order to get an accurate reading. "In the case of a mammogram where we see the lymph nodes in the armpit, which is right near where we're getting the vaccine shot, those lymph nodes are like first responders. That's the front line and they'll get enlarged first," said Dr. Sobolewski.