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Study in Peer-Reviewed Journal Finds 42% of Women Surveyed Had ‘Heavier Menstrual Flow’ Than Normal After COVID-19 ‘Vaccination’


A new study published in the journal Science Advances finds that 42% of surveyed women with regular menstrual cycles bled more heavily than usual after being “vaccinated” against COVID-19.


In a new study published in Science Advances a team of researchers analyzing a survey of “menstruating people” (women of childbearing age) and “formerly menstruating people” (women on birth control, postmenopausal women, women on hormone suppressors), has found that 42.1% of respondents experienced “heavier menstrual flow” after receiving the COVID-19 “vaccines.” The study, which also found “66% of postmenopausal people reported breakthrough bleeding” after the COVID-19 injections, adds to a rapidly growing body of evidence showing that women must be warned of this poorly understood, yet possibly dangerous, adverse event.

For their study, the researchers, led by Dr. Kathryn Clancy, professor of anthropology at the University of Illinois Urbana-Champaign, and Dr. Katharine Lee, professor of anthropology at Tulane University, surveyed 39,129 women (i.e. menstruating or non-menstruating people…), recruiting respondents through social media platforms including Twitter, and—to a much lesser extent—Facebook and Instagram. The survey—available from April 7, 2021 until June 29, 2021—included women between the ages of 18 and 80 years old, all of whom were “fully vaccinated.” (I.e. the participants were surveyed at least 14 days after one or two required doses “as this was before boosters.”)

A chart from the study showing adverse events, including those specific to menstruation, after COVID-19 “vaccination.” Image: Clancy, et al. / Science Advances

As for results, the researchers report that—in Clancy’s words to science news outlet Technology Networks— their “key finding is that increased bleeding (heavier among menstruating people, and breakthrough bleeding among non-menstruating people) is real, mechanistically plausible and experienced by a significant number of people” after receiving the COVID-19 “vaccines.” Clancy told Technology Networks that the adverse event “is also now supported by several prospective studies that have also found the same thing.

Specifically, Clancy et al. found that 42.1% of respondents reported heavier menstrual flow after “vaccination.” The researchers also found that “Among respondents who typically do not menstruate, 71% of people on long-acting reversible contraceptives, 39% of people on gender-affirming hormones, and 66% of postmenopausal people reported breakthrough bleeding.” Furthermore, the researchers found “that increased/breakthrough bleeding was significantly associated with age, systemic vaccine side effects (fever and/or fatigue), history of pregnancy or birth, and ethnicity.

Image: Clancy, et al. / Science Advances

In regards to correlation with ethnicity, the researchers reported in their study their “main findings were that a heavier menstrual flow was more likely for those respondents who were of non-white race, were Hispanic/Latinx, were older, had a diagnosed reproductive condition, used hormonal contraception, had been pregnant in the past (whether or not they had given birth), were parous [having had produced children], or experienced fever or fatigue after vaccination.”

Despite the trend toward Hispanic/Latinx women, there were undoubtedly instances of the menstrual irregularities amongst white women as well. In fact, Lee and Clancy had their own, personal experiences with the adverse event.

“Dr. Lee and I had our own wonky period experiences post-vaccine,” Clancy told Technology Networks. “If Dr. Lee hadn’t pointed them out to me first, I may never have made the connection myself,” the researcher added. Clancy even said that “After I tweeted about [menstrual changes post “vaccination”] and the response was overwhelming, we designed a survey instrument that would allow us to capture these experiences as well as any factors that might make one more at risk of this side effect.”

Interestingly, the study authors even noted that “Vaccine trial protocols do not typically monitor for major adverse events for more than 7 days, and additional follow-up communications do not inquire about menstrual cycles or bleeding.” Therefore, “manufacturers had no way of addressing the extent to which this observation was a coincidence or a potential side effect of the vaccines,” the authors added.

Indeed, Technology Networks notes in its writeup on the study that “The 2020 COVID-19 vaccine clinical trials did not explore whether COVID-19 vaccines have any side effects on the menstrual cycle.” (Emphasis theirs.)

The authors also add that a secondary finding was “that there are key factors that increase the chance someone may have this increased bleeding phenotype – being older (for menstruating people – younger if postmenopausal), having been pregnant/had kids, [and] having a hyperproliferative reproductive condition.”

In response to the study several women online referred to their own experience with abnormal menstruation post COVID-19 “vaccination.” One German Twitter user (@bin_muede), for example, wrote in response to a tweet from Clancy that “I’ve now been vaccinated for the fourth time, and my period is still driving me crazy! approx. 80 – 120 ml (m-cup) a day, I can no longer leave the house.” The user added that she’s been experiencing this symptom since April of 2021 when she was “vaccinated” with the BioNTech injection.

Another “mom” on Twitter (@queens_parents) wrote in response to a New York Times report on the study that “Women have been reporting this for months, but instead public health policies ignored their concerns and wouldn’t permit exemptions from mandates while women were silenced, bullied, or forced to lose their jobs as the ‘progressive’ [New York Times] sat idly by in silence.”

One “dog mom” (@mandmdoglover) even wrote a sarcastic yet heartbreaking response to the Times report ragging on the way the outlet framed the story. “May affect menstruation but no cause for alarm?” the user tweeted. “Tell that my 3 nieces who have had miscarriages and are now struggling to conceive. Please.”

In response to Twitter comments like the ones immediately above Clancy seemed to—in general—confirm the existence of the adverse event, but downplay its severity. “We are looking at how long the effect lasts but so far all signs point to this affecting a minority of people, for one or two periods,” Clancy told one woman (@Ad_Richmond) who said she knows “2 ladies who still struggle with bad periods” which started after they received the COVID-19 “vaccines” in 2021. Clancy added that “We do know that people with underlying health conditions like endometriosis or fibroids are likely more at risk.”


Feature image: Marco Verch Professional Photographer

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