LOS ANGELES (NewsNation Now) — As women return to their physicians’ offices to catch up on routine tests that were delayed by the coronavirus pandemic, but in some cases, they’re met with one more pandemic surprise — a false red flag for breast cancer.

While most people are familiar with post-vaccination symptoms of a sore arm or slight fever — lymph nodes enlarged by the immune system’s response to the COVID-19 vaccine are also a sign that the shot is doing its job.

But the medical specialists who search mammograms for signs of malignancy, the unexplained appearance of swollen lymph nodes have typically sparked concern and a recommendation that the patient may be called back for further testing.

“Something that we see from time to time, we were seeing multiple times a day, raised alarm bells in our practice and breast radiology across the country,” said UCLA Medical Center Dr. Hannah Milch.

Specialists have alerted each other about the issue for the past few months, and as much as they want women to be informed, they also want to avoid undue stress and avoid missing signals that could be important.

According to the Centers for Disease Control and Prevention, the second dose of the Pfizer-BioNTech or Moderna COVID-19 vaccine will cause swollen lymph nodes in about 16% of people. The swelling usually happens within two days after vaccination, and it’s actually a good thing since the body’s immune system is reacting as it should. However, enlarged nodes in breast imaging can result in a false-positive mammogram.

“We’re trying to decrease anxiety among our patients and not call them all back for more imaging unless absolutely necessary,” Milch said.

There’s no formal data compiled yet, but radiologists are urging women to schedule breast screenings before vaccination or at an appropriate time after.

“Try to schedule your mammogram four to six weeks after your second dose of vaccine,” said Dr. Priti Shah, Virginia Commonweath University Health’s breast imaging director.

Another apparent vaccination issue for some women is a distinct change in their menstrual cycles.

“People have started their periods early and much, much heavier,” explained Dr. Tara Scott, with the Revitalized Medical Group.

But doctors say there’s no formal data on that yet, either, and there’s no evidence to suggest it’s directly linked to the COVID-19 vaccine.

“A lot of things in our lives can affect the menstrual cycle including stress, illness, and certainly immune response,” said OBFYN Dr. Stephanie Tootle, with Memorial Health. “And certain medications can be responsible for temporary missed cycles and shouldn’t be a concern if that does happen.”

As for mammograms, doctors stress their importance along with getting a vaccination.

So, women should be aware that timing for each is key. In general, mammogram before vaccination or six weeks after.