By Stephanie Stahl

PHILADELPHIA (CBS) — A surprising, newly discovered side effect of the COVID-19 vaccine is causing concern for women and has prompted new guidelines on the timing of mammograms. Doctors say women who receive the COVID vaccine can develop symptoms that are also associated with breast cancer.

Now women are being advised to space out the vaccine and their mammograms.

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The COVID-19 vaccines can cause lymph nodes to swell, which is also a potential sign of breast cancer.

“Most women are concerned about it because they have an enlarged lymph node and the first thing they think of is cancer,” said Dr. Andrea S. Porpiglia.

Dr. Porpiglia with Fox Chase says swollen lymph nodes can be felt in the armpit area in both women and men and have recently started showing up on mammograms in people who’ve been recently vaccinated.

“Is it a sign the vaccine is working?” asked CBS3’s Stephanie Stahl.

“Yes,” Dr. Porpiglia said. “It’s just a normal immune response. When you get the vaccine, your body is making more cells to help fight the virus and by doing so you’re going to have an enlarged lymph nodes.”

Swollen lymph nodes are happening in 15% to 20% of people who receive the COVID-19 vaccine. It goes away on its own.

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If the swelling is related to cancer there would be additional imaging and biopsies.

To make sure there’s no confusion, the Society of Breast Imaging says people should schedule mammograms either before they get the COVID vaccine or six weeks after.

“COVID vaccine does not increase your risk of breast cancer. This is just a normal response we’re seeing from the vaccine,” Dr. Porpiglia said.

The bigger concern is that people are skipping or delaying routine cancer screenings, fearing exposure to the virus even though precautions are taken to avoid that.

“I’m afraid that we’re missing cancers because people are scared to go to the doctors,” said Dr. Porpiglia. “I have a feeling in the next couple of years we’re going to see an uptick in cancer, breast cancer.”

The recommendation from the American Cancer Society is that women have yearly mammograms after the age of 45.

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Doctors say women need to understand that they can safely have the vaccine and mammograms, they just have to be spaced out.

Stephanie Stahl