Mammograms show swelling due to COVID-19 vaccine, radiologists say 'don't worry' Women planning to schedule their annual mammogram might want to consider the timing of their COVID-19 vaccines. KFSN FRESNO, Calif. (KFSN) -- Women planning to schedule their annual mammogram might want to consider the timing of their COVID-19 vaccines. More and more doctors see a side effect. The shots often cause enlarged lymph nodes in the armpit or near the collarbone, which can be mistaken as a sign of cancer. But if you've recently been immunized, medical experts say not to worry. "If it's within four weeks after your vaccination, then you have a higher chance of having enlarged lymph nodes on the side where you have the vaccine," said Dr. Hannah Milch, a radiologist and assistant clinical professor at the UCLA David Geffen School of Medicine.