While many of the side effects of a COVID vaccine are known and well publicised, thousands in the US think that they may have another side effect they were never warned about: unexpected changes in their menstrual cycles, writes NPR.
Though many researchers and gynaecologists say a causal link hasn't yet been established between the vaccines and the reported changes, that hasn't stopped the worry among some people. And so far, scientists haven't collected much data on whether or how the vaccines might affect a menstrual period.
Kate Clancy, a human reproductive ecologist and associate professor of anthropology at the University of Illinois Urbana-Champaign, and biological anthropologist Katharine Lee of Washington University School of Medicine in St Louis, hope to change that.
Clancy has centred her research for decades on uterine function, ovarian hormones and menstrual cycles, and Lee is also a data engineer; her current postdoctoral work includes “collaborations on physical activity and reproductive hormones across the lifespan in healthy adult premenopausal women”.
NPR says the pair has collected more than 140,000 reports from people who have noticed a change in their periods after vaccination and are formally documenting those cases in an open-ended study.
Clancy's interest was first piqued by her own experience. “My period after dose one was one of the heaviest I remember having ever in my life,” she says. She took to social media with her story, and five months later, people are still responding.
The individual stories, even in large numbers, are not enough to prove vaccines are causing changes to menstruation. A healthy menstrual cycle is a complex hormonal process varying from person to person and month to month and is affected by many factors.
The Food and Drug Administration and all three manufacturers of US-approved vaccines tell NPR they have not seen evidence that the COVID-19 vaccine is causing menstrual irregularities — let alone health problems related to menstruation or fertility. The American College of Obstetricians and Gynaecologists says it is aware of the reports, but that vaccination is highly recommended and there is no reason to schedule vaccination around periods or other menstrual events.
“Obstetrician-gynaecologists and other women's health care practitioners should lead by example by being vaccinated and encouraging eligible patients to be vaccinated as well,” the association says.
Nonetheless, the outpouring of concern among women points to a blind spot in how clinical research on the COVID-19 vaccines was done. As with many other vaccine trials, the early COVID-19 studies did not ask much about reproductive health aside from questions around pregnancy. “It seeds doubt,” Lee says. “It makes people feel their bodies were not considered in part of the [clinical] trial.”
The Centers for Disease Control and Prevention is giving the issue a closer look. A CDC spokesperson told NPR that the agency was reviewing reports from one of its databases, the Vaccine Safety Datalink, to see whether it was possible to detect how the vaccine might affect menstruation.
The multitude of stories represents just a small fraction of the many tens of millions of people who have been vaccinated against COVID-19. Most have not experienced changes to menstruation, including women in the clinical trials, according to statements to NPR from Pfizer, Moderna and Johnson & Johnson.
"We haven't really heard much concern about menstrual issues," says Dr Kathryn Edwards, a professor at Vanderbilt University School of Medicine who sits on an independent data monitoring committee for the Pfizer COVID-19 vaccine.
Edwards says the clinical trials would have picked up any issues that were truly dangerous, but relatively minor or unusually rare changes to menstruation might be missed, she conceded. Participants in the clinical trials are handed a checklist asking about minor side effects like headaches or arm soreness, but there aren't any specific questions such as, "Are your menstrual periods irregular? Is your flow heavier?"
Because this data isn't collected, trial participants must report changes to menstruation as "adverse events" — that could cause the trials to miss relatively minor disruptions, she said.
But proving whether or not it's possible the vaccine could cause a minor menstrual disruption is difficult because periods can be so variable from person to person, says Dr Laura Riley, chair of obstetrics and gynaecology at New York-Presbyterian/Weill Cornell Medical Center in New York City.
“The menstrual cycle itself is just so incredibly difficult to study, because there are so many other things that may impact it," she says. "Just even thinking about how you would design that study is mind-boggling."
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