LOUISVILLE, Ky. —The COVID-19 vaccine rollout is underway, and doctors now warn about a recently discovered side effect that could cause needless worry.

What You Need To Know

  • Some who receive the COVID-19 vaccine experience swollen lymph nodes

  • Swollen nodes are a symptom of other ailments, including cancer

  • Doctor say this is normal

  • If you are concerned, contact your physician

Some people experience swollen lymph nodes at the injection site, which may be mistaken for various forms of cancer.  But actually, this is merely the body's response to the vaccine. Dr. Jason Smith, Chief Medical Officer at UofL Heath, described his own experience with this phenomenon.

"I've had a lot of lymph nodes swollen in my neck, in my arm, and underneath my arm after the injection and it was just on the side I had received the injection on," Smith explained that this is quite normal; it means the vaccine is working. He said, "(It's) Just your body's immune system producing the cells and the antibodies to fight the COVID infection, which is what we want, right? And so that is a good sign that means you are having a good response to the vaccine."

Smith also understands how scary finding a swollen lymph node can be for women, which can be a sign of breast cancer.

"You are talking about lumps in your arm, armpit, on your arm, or your chest wall, and so you could mistake that possibly for a mass," Dr. Smith said.

After a few days, things returned to normal for Dr. Smith, but he's encouraging folks to talk to their doctor if things don't clear up or they have additional concerns.

"If it is related to the vaccine, it should be self-limited, so it's something to keep in mind and look for, obviously. If it comes and goes, then we are ok. If it doesn't go away, that's the sign that you need to talk to somebody, particularly after about five to seven days."

Smith also says both the Pfizer and Moderna vaccine can produce this side effect.