New Study Links COVID-19 Vaccines To Temporary Changes In Menstrual Cycles
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If you’ve noticed unexpected changes in your menstrual cycle after receiving the COVID-19 vaccine, a recent study has found that you’re not alone. 

According to the survey, published in the Science Advances journal, 42 percent of people who said they had a regular menstrual cycle reported that they bled more heavily than usual after being vaccinated. Fourty-four percent noticed no change and around 14 percent reported a lighter period.

Nonmenstruating people — or those who are premenopausal or using long-acting reversible contraceptives and/or continuous hormonal contraceptives, experienced breakthrough bleeding after receiving the vaccine. 

From April to October 2021, researchers surveyed 39,000 subjects between the ages of 18 to 80 years old who do or used to menstruate in order to understand the possible effects the COVID-19 vaccine may have on their period. The participants were fully vaccinated with Pfizer, Moderna, AstraZeneca, Johnson & Johnson, or Novavax and had not previously contracted COVID. 

The inspiration behind the research came after the study’s co-author Katherine M.N. Lee and her colleague noticed conversations surfacing online and among close friends regarding unexpected changes in their periods after receiving their vaccines. The biological anthropologist at the Washington University School of Medicine in St. Louis recalls having the “worst cramps of my life” following her vaccination. 

“I think it’s important that people know this can happen, so they’re not scared, they’re not shocked and they’re not caught without supplies,” Lee said. 

Another study co-author, associate professor of anthropology at the University of Illinois, Kathryn B. H. Clancy, notes that the nature of the survey is “to provide evidence to better study these trends further” and is not a full representation of the general population. She also cautions that the study did not compare the results with a control group of people who were not vaccinated. 

Other notable standouts from the study found that some demographics were more likely to experience menstrual changes. For example, people who were older were more likely to have a heavier menstrual flow, along with those who used hormonal contraceptives, were previously pregnant, or had been diagnosed with fibroids, endometriosis, or polycystic ovarian syndrome.

Clancy and Lee’s work aims to spark new studies that explore the possible connections between vaccinations and shifts in menstrual cycles and in turn, improve medical transparency. 

“If you want to improve trust in government, trust in pharmaceutical companies, trust in medicine, trust in vaccines, then you have to take the time to do the work, so people know what to expect going into it,” Clancy said. “That effort makes people more likely to get their second shot or booster.”

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