Lack of Data on Covid-19 Vaccines and Periods Inspired Two Feminist Scientists to Learn More

A long history of dismissing women’s experiences in medicine may be limiting reported side effects in clinical trials

a Black woman wearing a blue sleeveless top receives a bandaid after receiving a vaccination from a white-appearing woman whose face is away from the camera
a Black woman wearing a blue sleeveless top receives a bandaid after receiving a vaccination from a white-appearing woman whose face is away from the camera
Photo by CDC on Unsplash

Vaccine trials include tens of thousands of people in phase 3 to ensure that even rare side effects are more likely to be detected. But once the vaccine is authorized and millions of people have begun receiving it, sometimes researchers learn about other even rarer side effects not captured in the trials. But scientists could also miss a side effect if they simply don’t ask about it — or don’t record it when participants report it.

That may be why it’s taken months after the vaccines were authorized by the FDA to explore whether changes in menstruation might be a temporary side effect of the Covid-19 vaccines. It took two feminist scientists and a large social media platform to even get the possibility on people’s radar.

“Nobody thought to ask about it as a part of routine part of [trial] questionnaires,” said Katharine Lee, PhD, a postdoctoral scholar in the Washington University School of Medicine Division of Public Health Sciences. “It’s frustrating as somebody who thinks a lot about these biological processes. Why wouldn’t you think to specifically ask about these [menstruation irregularities] as symptoms?”

It’s important to emphasize right at the start that investigating a possible link between Covid-19 vaccines and temporary changes in periods after vaccination does not mean the vaccine could affect fertility. The vaccine does not interfere with fertility or future pregnancy, and there is no evidence to support the misinformation that it does, despite the fact that it persists. But there are biological reasons that could explain why temporary changes in menstruation could occur after a vaccine without harming fertility, if it turns out that is happening.

It was after Lee got her first dose of the Pfizer vaccine and compared notes on side effects with a friend that the topic came to her attention. She started her period shortly after getting the vaccine — a surprise since her IUD usually prevents monthly periods — and her friend similarly experienced an irregular period. So Lee reached out to her dissertation advisor, Kate Clancy, PhD, an associate professor of Anthropology at the University of Illinois in Urbana-Champaign who has long studied menstruation in a variety of contexts. Clancy was intrigued, but she hadn’t heard anything about irregularities in menstruation as a side effect of the vaccine.

Then a few weeks later, Clancy received her first Moderna shot. Nine days later she had a much heavier period than usual.

“It went from I’m not menstruating to I’m just gushing,” said Clancy, who had otherwise been experiencing slower lead-ups to her period as she’s gotten older. “By day two, I was still changing out pads every hour and very grateful to be working from home.” She finally asked on Twitter whether anyone else was having the same experience. The response was — and still is — overwhelming. “That thread is still just going bananas,” she said.

None of the Covid-19 vaccine clinical trials have listed changes in menstruation as a possible side effect of the vaccine. However, no questions have been directly asked about it either, and it may be that participants didn’t report it or that clinicians did not record it when it was reported.

Lee and Clancy believed the possibility deserved further examination, so they designed an exploratory research survey to collect data on people’s experiences and hopefully determine what further research, if any, might be helpful. Any menstruating or formerly menstruating person, regardless of whether they had any irregularities, can sign up and report what they experience following any dose of any of the vaccines.

When the women submitted their research proposal for Institutional Review Board approval, they wrote that they anticipated 500 participants. “We hit that in the first couple hours,” Clancy said. The number of respondents has now surpassed 13,000.

Medicine’s history of disregarding women’s health

Given the tremendous response to the survey and the unending replies to Clancy’s original tweet, it might seem strange to people unfamiliar with clinical trials that such a widespread experience has not even been mentioned in reports about Covid-19 vaccine side effects, even if just to say it’s not a common experience. But the absence of any discussion about menstruation irregularities in the trials speaks to a larger systemic problem in medicine that dates back to the earliest days of research: a dismissal of women’s lived experiences.

The refusal to investigate women’s experiences in the U.S. was actually codified in 1977 when a U.S. Food and Drug Administration policy recommended excluding all women of childbearing age from phase 1 and 2 drug trials — regardless of whether they were using contraception, in a relationship, heterosexual or had a husband who was vasectomized. The reasons for the exclusion were understandable, arising in part from pharmaceutical disasters like that of thalidomide, which causes limb deformations in children exposed to it in the womb. But the over-cautious approach went too far and created an even bigger problem: a complete lack of data on how different drugs affect women. Although the National Institutes of Medicine began encouraging researchers to include women in trials starting in 1989, it wasn’t until 1993 that it became federal law for NIH-funded studies to include women and minorities in clinical trials.

But requiring women to be included didn’t change the culture of exclusion immediately.

“One of the overarching things about this issue is that it’s just not in the suite of questions we think about asking for side effects because the people who have decided the list of things we ask about traditionally have been tending more towards upper middle class white men in the history of medicine in the United States,” Lee said. “I do think that maybe we should think more about the experiences of a lot of different folks. Maybe this thing that happens to so many people once a month should maybe be considered more broadly across a lot of parts of medicine.”

Women’s health concerns have a long history of being disregarded or labeled “hysterical,” a word that literally comes from the Latin word hystericus, meaning “of the womb.” As more women have entered medicine and medical research as careers, that culture has slowly been changing, but it hasn’t been eradicated. The fact that so many women tried to report changes in their period after receiving Covid-19 vaccines and were dismissed is evidence of that, Clancy said.

“A lot of times when women report changes with their period, we are told when there’s variation in our bodies that it must be some kind of internal failing,” Clancy said. “There must be something going on within us. We are stressed, we are hysterical.” In fact, another scientist even accused Clancy of spreading “hysteria” by choosing to investigation whether menstrual changes might be related to vaccine administration.

“Are people who document sore arms and fevers and fatigue also fear-mongering?” Clancy asked. “I think that’s the question we need to ask: Why is it that when it’s related to periods, it’s fear-mongering. but when it’s any of these other broad systemic effects, we don’t consider it fear-mongering?”

Clancy is clear that she and Lee are investigating the topic without assuming there is a causal connection to vaccination and with the expectation that any effect is temporary and not a reason for concern.

“We are looking at something that’s fairly transient,” she said. “You don’t have to be terrified if you get one really wonky period or two. That’s why it’s important to study it.”

People were reporting it but no one was listening

Lee and Clancy both said that finding out whether irregularities in menstruation could be a potential side effect of a vaccine could help people be prepared for it and not worry when it happens.

“If this isn’t something that’s specifically asked about, then people aren’t going to think to report it necessarily,” Lee said. “It does seem like it should be part of the standard set of questions we ask when we’re testing vaccines in healthy adults. For me, it comes down to making sure that people who might experience menstrual bleeding after the vaccine know that it might occur after the vaccine, especially if they are perimenopausal or on hormone suppressing medication.”

At the same time, however, many people did apparently report it, or tried to, and were not taken seriously, Clancy said. She said she receives five to 10 emails a day from people who saw her tweet and reached out to say they were having a similar experience.

“Most of those emails are by people who said, ‘I tried to tell somebody about my experience and they told me that I was wrong,’” Clancy said. “Part of the reason that we are finally only now, months later, noticing that this might be something that menstruators are experiencing is that people hadn’t been listening until now.”

That reality has informed the purpose of the pair’s research.

“A lot of the work of feminist biology is testing assumptions,” Clancy said. “One of the big assumptions I noticed was a lot of people who were telling me they had these experiences were saying, ‘I did talk to my doctor and my doctor said, “Oh, it’s just stress.” Or I did try to tell somebody and they laughed at me about it. My feminist biology spidey sense tingles when some doctor tries to tell a menstruator in particular that their lived experience isn’t real.”

Clancy even received an email from a woman currently in a vaccine trial who tried to report weird period symptoms and was initially told it was just stress. The clinician refused to enter the symptoms in the woman’s chart. After a second unusual period, the woman tried again to report it but was told it was only because she was perimenopausal. The woman insisted over the clinician’s objections that her symptoms be included in her chart.

Giving a space for people to share their experiences is therefore a central part of the survey’s intentions, regardless of what the scientists discover.

“As feminists, we want to pay attention to the lived experience of people,” Clancy said. “We really want to bear witness to this experience and have some of these people have experiences where someone is just listening and recording their information and not belittling them.”

That means hearing from those who have had unpleasant or unexpected symptoms as well as those who did not experience any changes at all. So far, she has heard from people with early or heavy periods, people whose period stopped temporarily, people whose period came late, and people who didn’t see any changes at all in menstruation. The survey includes questions about respondents’ menstrual cycle timing and history of bleeding disorders or autoimmune disease, what vaccine they received, and whether they’ve had Covid, among other questions.

“We do think there’s an under recognized sense that most people who menstruate know that lots of things can influence cycles of symptoms,” Lee said. Experiencing higher stress levels in general, for example, can affect periods. “It’s not unreasonable that a vaccine that evokes such a strong immune response — with people experiencing headache, fatigue, fevers, and soreness of shoulders when compared to other vaccines — that the uterus or endometrium might also be responding to this immune stressor for a short period.”

Exploring possible mechanisms

Jen Gunther, an OBGYN who writes The Vajenda at Substack, took a deep dive into the possible mechanisms that might explain a link between Covid-19 vaccination and menstruation if it does turn out that there’s an association — something that hasn’t yet been shown conclusively. She also expressed frustration at how women’s issues are often ignored, and her discussion of biology is well worth the read.

Clancy mentioned two potential biological mechanisms that she’s aware of. One came from her discussions with Anirban Sen Gupta, PhD, a platelet researcher at Case Western Reserve University who will be collaborating with Lee and Clancy.

Sen Gupta told Clancy that some research has a possible link between the nanoparticles used in the mRNA vaccines and a temporary reduction in platelets count. Platelets are the blood cells that help blood clot, so it’s possible that fewer platelets could lead to heavier bleeding — less clotting — in someone having a period, Clancy said.

“If you’re a menstruator and your period is due soon anyway, then you might kind of have some kind of bleeding event that is much more powerful than what you would normally have just because your body is not quite as effective as at coagulating your blood,” she said.

The phenomenon of lower platelet counts is called thrombocytopenia, and it is already a known rare side effect of the measles-mumps-rubella (MMR) vaccine. The condition is not life-threatening and resolves on its own without any long-term side effects. Clancy emphasized that it’s important that people don’t worry that heavier bleeding after a vaccine suggests any concerns about fertility or other systemic issues.

Another possible mechanism is the normal immune activation that occurs as a result of a vaccine,” Clancy said. Her lab has previously studied how systematic inflammation can be associated with changes in hormone concentrations and other temporary effects on the reproductive system. Inflammation essentially refers to the immune system taking notice of a perceived threat and responding to it. Clancy’s lab has found that people with higher levels of C-reactive protein (CRP), a biomarker for inflammation, tend to have lower levels of estradiol and progesterone concentrations.

“What we could be seeing here is, again, another transient response to your immune system getting a pretty good kick,” Clancy said. “A vaccine is activating your immune system. It’s going to create some inflammation.”

The uterus might be particularly sensitive to temporary inflammation because it’s such a dynamic environment.

“The thing that’s so cool about the uterus is that it’s a site for where tons and tons of tissue remodeling is happening all the time,” Clancy said. “It’s constantly making new tissue and constantly differentiating tissue. So if you have some other major inflammatory thing happening in the body, you can imagine it might mess with some with some tissue remodeling.”

Neither Lee nor Clancy has any concerns about the vaccine if it turns out temporary menstrual changes are linked to it. What’s most important, they said, is helping people know one way or another whether to expect it as a possibility so that it doesn’t raise alarms that some other problem is occurring and so that people can be ready for it.

“It just would be nice to know about,” Lee said. “Making sure that everyone knows what might happen after a vaccine is important.”

If you would like to participate in Lee and Clancy’s study, you can do so here.

Tara Haelle is a science journalist, public speaker, and author of Vaccination Investigation and The Informed Parent. Follow her at @tarahaelle.

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