News A side effect of the COVID-19 vaccine can mimic a sign of breast cancer. This is normal, doctors say. February 26, 2021 Adrianna Rodriguez, USA TODAY Comments Off on A side effect of the COVID-19 vaccine can mimic a sign of breast cancer. This is normal, doctors say. Doctors recommend scheduling a mammogram before receiving a COVID-19 vaccine after some have been mistaking swollen lymph nodes for breast lumps.