Thousands Report Unusual Menstrual Patterns After COVID-19 Vaccination | Science

Kathryn Clancy received her first dose of a COVID-19 vaccine in early 2021 and 10 days later found herself sitting uncomfortably in a Zoom work meeting during one of the heaviest times she has ever had. known. “I had what is often called menstrual flooding,” says Clancy, a biological anthropologist at the University of Illinois, Urbana-Champaign. Clancy wouldn’t have thought to connect the experience to the dose of Moderna she received were it not for her graduate student, Katharine Lee, now at Tulane University, who shared a similar story. “I had the worst cramps of my life” after the COVID-19 vaccination, Lee says. Intrigued, Clancy – who didn’t experience such intense symptoms after her second dose – shared her story on Twitter. Hundreds of people responded with side stories, leading him to suspect a potential link to vaccination.

These suspicions grew with the completion of a more formal survey in which Clancy, Lee and colleagues collected thousands of stories of breakthrough bleeding and heavier bleeding after a COVID-19 vaccine from people around the world. Between April and October 2021, the survey welcomed anyone aged 18 and over who has or used to menstruate. Because of this, Clancy warns, the percentage affected is likely not representative of the general population – and indeed a whopping 42% of around 16,000 people in the survey who had a regular menstrual cycle said that they were bleeding more heavily than usual after vaccination, a much higher number than others have reported. Yet researchers have captured a wide range of people and their stories, including populations often overlooked in research on menstruation and breakthrough bleeding, which happens when you least expect it, such as transgender and menopausal people. .

Clarifying the issue is vital. “It’s important to know,” says Victoria Male, a reproductive immunologist at Imperial College London. “Let’s say you got the shot and the next day you felt really bad like some people do.” If you hadn’t been told about the risk of fever, muscle aches and other effects that quickly dissipate, “you’d be really worried,” she said. Highlighting the risk of menstrual irregularities and confirming that they are not a health risk also helps combat widespread misinformation that COVID-19 vaccines impair fertility, according to Male and others.

“We need those studies there because it elevates the issue,” says Alison Edelman, an obstetrician-gynecologist at Oregon Health & Science University who was not involved in this research but looked at menstrual irregularities after vaccination. against COVID-19.

After Clancy’s initial tweet elicited such a response, she and Lee set out to find out more, initially targeting a survey of 500 people about menstrual experiences after COVID-19 vaccination. When 500 people signed up within the first hour after the survey went live, Clancy realized the project was going to explode way beyond what she had expected.

More than 165,000 people worldwide who have been vaccinated with two doses have participated. (Boosters weren’t widely available during the investigation period.) Today, the team reports in Scientists progress on a subset of 39,000 from its first set of analyses. (The paper was published in February as a preprint.)

Given their background in anthropology, Clancy and Lee focused their investigation on eliciting narrative-style responses and documenting symptoms, such as breakthrough bleeding, that are significant but can be difficult to measure quantitatively. In postmenopausal people, unexplained vaginal bleeding is a symptom of uterine cancer, so it occurring after a dose of vaccine may cause unnecessary concern. In survey results released today, 66% of 673 postmenopausal people reported breakthrough bleeding, as did 39% of 280 people on gender-affirming hormones. Because of these hormones that this latter group takes, many don’t have periods and may find it distressing to get one.

The survey results, even with the authors’ caveats, could raise concerns that the risk of menstrual irregularities after vaccination is much higher than it actually is, worries Lill Trogstad, obstetrician- gynecologist and epidemiologist at the Norwegian Institute of Public Health who was not involved in the study. In addition to likely attracting people who had experienced these problems, the study did not include surveys of a control group of unvaccinated people or compare pre-vaccination menstrual cycles with post-vaccination cycles among respondents over time. “Those two things kind of limit the study,” says Trogstad. “You cannot estimate the excess risk after a vaccine” without a control group. Its own survey, conducted via smartphones and published as a preprint, found that just over 13% of young women in Norway said their periods were heavier after vaccination against COVID-19; this compared to 7% of the same group who said their periods before vaccination were heavier than normal.

Clinical trials of COVID-19 vaccines have not looked for effects on the menstrual cycle. Whatever the prevalence of menstrual irregularities after vaccination against COVID-19, scientists note that there are hypotheses that could explain it. Much like infections and fevers, which are known to affect menstruation, the immune system’s response to vaccination can alter sex hormone patterns or cells that build up and break down the uterine lining, both of which are linked to immunology. There has been little research on other vaccines and periods, but a study from Japan found an association with the human papillomavirus vaccine and irregular menstruation.

The eruption of anecdotes about menstrual irregularities after a COVID-19 vaccine, and the resulting misinformation that vaccines could impair fertility, have spurred more studies of menstruation than the neglected subject usually receives. . A March preprint by Male found an effect on cycle length but not menstrual flow after vaccination in a small study of 79 people. A study this week of premenopausal women found a temporary increase of half a day to 2 days, on average, in cycle length after a COVID-19 vaccine.

In her work, Edelman relied on anonymized data from a fertility awareness app. She found that, on average, vaccination changed cycle length by less than a day, but those who received both doses of the vaccine in the same menstrual cycle had an average difference of 2 days. About 10% of these people, who received both doses of the vaccine in the same cycle, saw a change of at least 8 days in their cycle length, but they seem to return to their baseline level as soon as one cycle later. “We have this picture coming together that’s very reassuring,” Edelman says of these and other studies showing the vaccine doesn’t 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 having volunteers track and report symptoms in real time, rather than relying on memory, as this survey did. But she was unable to secure funding for such an effort. She is also interested in studying the phenomenon after influenza vaccination. In the meantime, her team is completing a follow-up survey on how quickly menstrual patterns renormalized for respondents. “Our goal is to start from the position of believing the people who talk to us,” she says, and let that guide future studies.

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