Vaccine timing and mammograms

A sore arm, fatigue, fever and chills are all known as possible side effects of the COVID-19 vaccine. However, a lesser known side effect could result in a false positive on a mammogram.

“Some patients who have been recently vaccinated may experience axillary adenopathy, also known as swollen lymph nodes, in the armpit,” says Dr. Patricia Poole, a radiologist affiliated with Sharp Coronado Hospital. “This could be confused as a possible sign of breast cancer for those who have a mammogram after being vaccinated.”

Both the Society of Breast Imaging (SBI) and the Centers for Disease Control and Prevention (CDC) have reported that swelling or tenderness in the armpit was a recognized side effect during clinical trials of the Moderna and Pfizer vaccines. For patients receiving the Moderna vaccine, nearly 12% reported swollen lymph nodes after the first dose, and 16% after the second dose. In the Pfizer COVID-19 vaccine trial, the side effect was reported in 58 more cases in the vaccinated group than in the placebo group.

The inflammation is a normal response of the immune system to the vaccine and suggests that antibodies are at work protecting against the virus that causes COVID-19.

According to Dr. Poole, having a mammogram soon after vaccination may cause unnecessary worry about swollen lymph nodes. These results are to be expected and are not normally of concern.

“Patients can plan accordingly,” says Dr. Poole.

The SBI recommends routine screening mammograms be performed either before receiving the first vaccine dose or 4 to 6 weeks after the second dose due to a temporary effect that the vaccine can have on the appearance of lymph nodes.

However, diagnostic mammograms for palpable masses or other clinical symptoms should not be delayed. “If you find a new lump or concern, you should not delay your health care,” adds Dr. Poole.

“Along with getting vaccinated for COVID-19, it’s also important to come in for your mammography screening when it is recommended,” says Dr. Poole. “Regular screening mammograms lead to early detection of breast cancer.”

Sharp Coronado Hospital offers online scheduling for mammography.