People Are Saying The COVID Vaccine Is Messing With Their Periods

• People are reporting heavy, painful periods on social media, saying they believe their menstrual cycle was disrupted by the COVID vaccine.

• However, gynecologists caution that it's too soon to say whether there's a connection.

• Generally, one irregular period is not cause for concern, say experts.

Over the past few months, a number of people have taken to social media to report heavy, painful periods, saying they believe their menstrual cycle was disrupted by the COVID vaccine.

To track this phenomenon, Dr. Kate Clancy, a biological anthropologist and associate professor at the University of Illinois at Urbana-Champaign, is administering an open survey to compile qualitative menstrual data.

"A colleague told me she has heard from others that their periods were heavy post-vax. I'm curious whether other menstruators have noticed changes too?" she asked in February via tweet, a month before launching her survey. "I'm a week and a half out from dose 1 of Moderna, got my period maybe a day or so early, and am gushing like I'm in my 20s again."

Her original tweet has been shared almost a thousand times, with people replying with their post-vax menstrual changes, like post-menopausal bleeding and early periods starting days after the shot.

However, gynecologists caution that it's too soon to say whether there's a connection.

"The data that’s out there that I’ve seen is anecdotal, and none of it is controlling for women who have not gotten the vaccine," says Dr. Margaret Polaneczky, a gynecologist at Weill Cornell Medicine in New York. "There are very few conclusions we can make based on self-reports other than to say, it’s something we should look into more closely.”

Are there any studies about the COVID-19 vaccine's effect on menstrual cycles?

Dr. Jen Gunter, author of The Vagina Bible, says there's no hard data yet. During clinical trials for the COVID vaccines, there was nothing to suggest that menstrual disruption could be a side effect.

In her own reporting on the subject, Dr. Gunter reached out to "one of the principal investigators from Pfizer to see if they tracked the data for their COVID-19 vaccine" and didn't hear back. Beyond the COVID vaccine, she looked into whether investigators tracked menstrual data in other vaccine studies, like the HPV vaccine (Gardasil) and Rubella. One of the Gardasil researchers told her he couldn't find any menstrual data, but a 1987 Rubella vaccine study showed that side effects of the Rubella vaccine were higher during the second half of the menstrual cycle.

"I don’t know if it’s because it wasn’t asked [in the COVID vaccine studies], or because women didn’t report it," Dr. Polaneczky adds. "At this point, we need to be really careful about presuming cause and effect. Menstrual abnormalities are incredibly common at any given time." Things like stress (hello, ongoing pandemic), weight fluctuations, thyroid problems, certain medications, undiagnosed pregnancies, and early menopause can throw your cycle out of whack. "In any given time frame, you’re going to have a lot of women who also experience menstrual abnormalities," Dr. Polaneczky continues. "So we need to be careful not to presume cause and effect when what we’re looking at is coincidence in timing."

Considering that older people and people with medical conditions were prioritized in the vaccine rollout nationwide, Dr. Gunter notes that "there’s a possibility that people who are more likely to have irregular cycles actually got the vaccine first," in January, February, and March. People with medical conditions, people on certain medications, and people in their forties are already more likely to experience irregular periods than healthy twenty-somethings and thirty-somethings, who are getting the vaccine now.

Dr. Gunter also notes that the people self-reporting tend to be the loudest voices in the room, which might give off the impression that more people are experiencing menstrual changes than there truly are: "People are noticing their menstrual cycles change, but all the people who aren’t noticing a change aren’t saying anything."

Sooo, what could be causing erratic periods?

Dr. Polaneczky explains that there are mechanisms in the reproductive system that are closely tied to the immune system. Like other vaccines, the COVID vaccine generates inflammatory molecules called cytokines and interferons. "We know that the endometrium of the uterus has receptors for these molecules and is a very active immunoresponsive organ," Dr. Polaneczky says.

For example, in order to become pregnant, the immune system has to suppress itself in order to allow an embryo to implant. The hormones that control these mechanisms change throughout the menstrual cycle. "One could postulate, perhaps, that the inflammatory response from the vaccine is somehow interacting with the immunological mechanisms that are ongoing in the uterus and disrupting them in some way," Dr. Polaneczky says, though she personally doubts it. "If that’s the case, I think we should have seen it in the vaccine trials, and I think we would see it with other vaccinations [aside from the COVID vaccine]. So far, we haven’t." This might sound scary, but it's nothing to worry about.

"Let’s say this is true, that it is a vaccine side effect, there’s no evidence that it’s concerning," Dr. Gunter says. "The endometrium is built to respond just like you’re built to have a fever." In other words, the body is responding exactly the way it's supposed to, and it's likely a single-cycle event. (Remember, the physical stress of having a cold or the flu could change your period even during non-pandemic times.)

And just to be clear: Despite the rumors swirling on social media, the COVID vaccine doesn't cause infertility. The American College of Obstetricians and Gynecologists (ACOG) calls claims linking the COVID-19 vaccine and infertility “unfounded” and “scientifically disproven.”

There's also a possibility that the experts running the vaccine trials weren't paying attention to periods up until this moment. "There’s an ongoing, appropriate criticism that science tends to ignore the fact that there’s half the population who have a menstrual cycle that could be impacted," Polaneczky adds.

What should I do if I notice menstrual cycle changes after getting the COVID-19 vaccine?

If your period is slightly off, don't panic. However, you should talk to your doctor right away if you're 1) pregnant and experiencing abnormal bleeding, 2) hemorrhaging or experiencing incredibly heavy bleeding, or 3) post-menopausal and bleeding.

"In those situations, you'd need to get in touch with your doctor immediately and always make sure they do a pregnancy test if you're experiencing a different bleeding pattern and there's a chance you could be pregnant," Dr. Polaneczky says. "Other than that, if it's something like spotting or a slightly late or a slightly early period, it can probably be watched through a cycle, and if it persists throughout the following cycle, see your doctor."

Generally, one irregular period is not cause for alarm. "We really only tell people to let us know if [an irregular period] happens several months in a row or it’s happening multiple times during a year," Dr. Gunter says. "A one-off isn’t medically concerning."

However, there is concern that stories of early or heavy periods might prevent women from getting the vaccine.

"I think we need to be really careful how we discuss it so we don't frighten women with a theoretical concern," Dr. Polaneczky says. "I'm not advising women anything differently based on these anecdotes." In other words, there's no reason not to get the vaccine.

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