Thousands of women report unusual periods after COVID-19 vaccination

(ORDO NEWS) — Katherine Clancy received her first dose of the COVID-19 vaccine in early 2021, and 10 days later found herself uncomfortable sitting in a work meeting in Zumma during one of the heaviest periods she had ever experienced.

“I had what is often called menstrual flooding,” says Clancy, a biological anthropologist at the University of Illinois at Urbana-Champaign.

Clancy would not have thought to link these sensations to the dose of Moderna she received were it not for her graduate student Katherine Lee, now at Tulane University, who told a similar story.

“According to Lee, after getting the COVID-19 vaccine, I had the worst seizures of my life.” Intrigued, Clancy, who didn’t experience the same severe symptoms after her second dose, shared her story on Twitter.

Hundreds of people responded to her with similar stories, leading her to suspect a potential connection to the vaccine.

Those suspicions have intensified since the completion of a more formal study in which Clancy, Lee and colleagues collected thousands of stories of breakthrough bleeding and more severe bleeding after the COVID-19 vaccine from people around the world.

In the period from April to October 2021, everyone aged 18 years and older who had or had a period took part in the survey. Because of this, Clancy warns, the percentage affected is likely not representative of the general population.

Indeed, 42% of the approximately 16,000 people in the survey who had regular menstrual cycles said they bled more than usual after vaccination, much higher than other researchers report. However, researchers have covered a wide range of people and their histories, including populations,

Clarifying this issue is vital. “This is important to know,” says Victoria Meil, a reproductive immunologist at Imperial College London. “Let’s say you get a vaccine and the next day you feel terrible, as some people do.”

If you hadn’t been informed of the possibility of fever, muscle aches and other effects that would pass quickly, “you would be very worried,” she says.

Highlighting the possibility of menstrual irregularities and confirming that they are not a health risk also helps combat widespread misinformation that COVID-19 vaccines impair fertility, Meil ​​and others say.

“We need studies like this because they raise an issue,” says Alison Edelman, an ob/gyn at the Oregon Health and Science University, who was not involved in this study but studied menstrual irregularities after COVID-19 vaccination.

After Clancy’s first tweet sparked such a response, she and Lee decided to find out more, initially aiming to survey 500 people about their periods after the COVID-19 vaccine. When 500 people signed up for the survey within the first hour of posting it online, Clancy knew the project was going to swell far more than she had anticipated.

More than 165,000 people worldwide who received two doses of the vaccine took part in the survey. (Today in the journal Science Advances, the team reports the results of the first round of a subgroup analysis of 39,000 people. (The paper was published in February as a preprint.)

Given their anthropological background, Clancy and Lee focused their research on getting answers in a narrative style and on documenting symptoms such as breakthrough bleeding, which are important but difficult to quantify.

Among postmenopausal people, unexplained vaginal bleeding is a symptom of uterine cancer, so its occurrence after a vaccine may cause unnecessary concern. In a study published today, 66% of 673 postmenopausal people reported breakthrough bleeding, as did 39% of 280 people taking sex-confirming hormones.

Due to the hormones that the latter group takes, many of them do not have periods, and their appearance can cause discomfort.

The results of the study, even with the authors’ caveats, may raise concerns that the likelihood of menstrual irregularities after vaccination is much higher than it actually is, worries Lill Trogstad, an obstetrician and epidemiologist at the Norwegian Institute of Public Health, who was not involved in the study.

In addition to the fact that the study most likely involved people who experienced similar problems, it did not include interviews with a control group of unvaccinated people and did not compare the menstrual cycles of the respondents before and after vaccination over time.

“Those two things kind of limit the study,” Trogstad says. “You can’t estimate excess risk after vaccination” without a control group.

Her own poll conducted using smartphones and published as a preprint, showed that just over 13% of young women in Norway reported that their periods became more abundant after being vaccinated with COVID-19; this is compared to 7% of the same group who said their periods were heavier than usual before the vaccination.

Clinical trials of the COVID-19 vaccine have not studied its effect on the menstrual cycle. Regardless of the prevalence of menstrual irregularities after COVID-19 vaccination, scientists note that there are hypotheses that can explain this.

Like infections and fevers, which are known to affect periods, the immune system’s response to vaccination can alter the structure of sex hormones or the cells that build and break down the lining of the uterus, both of which are immunologically related.

Research on other vaccines and menstruation has been limited, but one study from Japan found an association between the human papillomavirus vaccine and irregular periods.

A spate of anecdotes about menstrual irregularities after COVID-19 vaccines, and the resulting misinformation that vaccines can interfere with fertility, have spurred more menstruation research than is usually given to this neglected topic.

In a preprint published in March, a small study of 79 people found an effect on cycle length but not menstrual flow after vaccination. A study this week on premenopausal women showed a temporary increase in cycle length by an average of half a day to 2 days after being vaccinated with the COVID-19 vaccine.

In her work, Edelman relied on anonymous data from a fertility app. She found that, on average, vaccination changed cycle length by less than 1 day, but for those who received both doses of the vaccine in the same menstrual cycle, the difference was an average of 2 days.

Approximately 10% of those who received both doses of vaccine in the same cycle experienced a cycle length change of at least 8 days, but returned to baseline after one cycle. “We’re getting a picture that’s very encouraging,” Edelman says of these and other studies showing that the vaccine does not affect fertility.

For his part, Clancy is keen to continue this research. She wants to study menstrual flow before and after COVID-19 vaccination by asking volunteers to track and report symptoms in real time, rather than relying on memory as in this study.

But she has not yet been able to obtain funding for such work. She is also interested in studying this phenomenon after influenza vaccination.

Meanwhile, her team is completing a follow-up survey on how quickly menstrual cycles returned to normal in respondents. “Our goal is to start from a position of faith in the people who talk to us,” she says, and to do further research on that basis.


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