KEY POINTS

  • The coronavirus vaccine may cause swollen lymph nodes
  • The side effects mirror signs of breast cancer
  • Experts recommend taking a mammogram before getting a shot or four weeks after the second dose

An alarming side effect to the COVID-19 vaccine is being reported among women after getting their shot of Pfizer and Moderna’s vaccines.

There have been recent reports of women finding big, painful lumps under the arm after receiving their COVID-19 shots. Swollen lymph nodes are a known side effect of the vaccine but may also mirror signs of breast cancer.

“I panicked, I’ll admit, initially ... I had a big, visible, painful lump,” Dr. Bridget Rogers told CBS4’s Kathy Walsh. Rogers is a radiologist specializing in breast imaging at Solis Mammography. 

“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 added. 

Dr. Rogers had just gotten her second dose of Pfizer’s coronavirus vaccine the day prior. While the bump "started to improve" after two days, she says there have been other reports of visibly enlarged lymph nodes from her colleagues. 

Researchers at the Pfizer-BioNTech vaccine trial reported 64 cases of swollen lymph nodes among its 2,000 vaccine recipients. 

Experts have advised patients who have received the novel coronavirus vaccine to reschedule their yearly mammogram screenings before receiving the vaccine or four weeks after the second dose to avoid confusion. 

Dr. Tan Yah Yuen, a breast surgeon at the Mount Elizabeth Hospital, warned that the swollen underarm lymph nodes could lead doctors to falsely suspect breast cancer. 

"If the clinical suspicion is that the swollen lymph node is due to the vaccination and not breast cancer, then a repeat ultrasound can be done in two to three months to follow up on the swollen lymph nodes for resolution," Yuen told The Straits Times

Swollen lymph nodes can be seen after the first or second doses. The side effects can also occur in men. The condition usually resolves itself within 10 days of getting a vaccine shot. 

Women who are in cancer remission are also advised to discuss their mammogram or ultrasound checks with their doctor. Yuen also recommended getting the vaccine jab on the opposite arm to prevent false alarms of recurrence. 

Breast scans are recommended for women above 50 who exhibit no signs of cancer Breast scans are recommended for women above 50 who exhibit no signs of cancer Photo: AFP / ANNE-CHRISTINE POUJOULAT