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Covid-19 mRNA vaccines are causing an unexpected side effect in biological women. The still-experimental messenger ribonucleic acid (mRNA) vaccines have been administered to 65 million Americans.

Commonly reported side effects include pain around the injection site, headache, fatigue, muscle pain, and death.

But some women are complaining of an unexpected side effect after the second dose: swollen, painful mammary lymph glands that can mimic breast cancer.

"I panicked, I'll admit, initially," said Dr. Bridget Rogers, radiologist at Solis Mammography.

"I had a big, visible, painful lump," she told CBS4 Health Specialist Kathy Walsh. Dr. Rogers said she received her second dose of mRNA vaccine the day before.

"I tried to reassure myself by remembering that this is actually a sign that the vaccine was doing what it's supposed to do, activating your immune system," she said.

Still, she admits she had an ultrasound done just to make sure.

"I've been trying to forewarn women ahead of time," said Dr. Stephanie Miller, a breast surgeon and Medical Director of the Breast Program at Rose Medical Center.

She tells women to let the mammography center know if you've recently had a vaccine "So that we can have the right explanation for what we're seeing."

Mammary lymph glands are located in the arm pit and neck on the affected side.

Swollen, painful lumps in the armpit and in the neck under the jawline are among the first signs of breast cancer in some women.

Doctors urge women not to take the vaccine if you have a mammogram scheduled the next day because it may trigger a false breast cancer reading.