Experts think COVID vaccines may be responsible for acute menstrual changes

Experts at the National Institutes of Health (NIH) have awarded one-year supplemental grants totaling $1.67 million to five institutions to explore potential links between COVID vaccines and menstrual changes, after thousands of women reported menstrual irregularities after vaccination.

According to the NIH website, some women have reported experiencing irregular or missing menstrual periods, heavier-than-usual bleeding and other menstrual changes after receiving COVID vaccines.

The new funding will go toward research to determine whether the changes may be linked to COVID vaccination itself, and how long the changes last. Researchers will also seek to clarify the mechanisms underlying potential vaccine-related menstrual changes.

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The year-long study will initially follow unvaccinated participants to observe changes that occur following each dose. Some groups will exclude participants on birth control or gender-affirming hormones, which may have their own impact on periods.

Researchers will assess the prevalence and severity of post-vaccination changes to menstrual characteristics, including flow, cycle length, pain and other symptoms. These analyses will account for other factors that can affect menstruation — such as stress, medications and exercise — to determine whether the changes are attributable to vaccination.

The five NIH-funded studies will be conducted by researchers at Boston University, Harvard Medical School, Johns Hopkins University, Michigan State University and Oregon Health and Science University.

The studies will likely incorporate between 400,000 and 500,000 participants –– including adolescents and transgender and nonbinary people, according to Dr. Diana Bianchi, director of the agency’s Institute of Child Health and Human Development, which is funding the research along with NIH’s Office of Research on Women’s Health.

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These “rigorous scientific studies will improve our understanding of the potential effects of COVID-19 vaccines on menstruation, giving people who menstruate more information about what to expect after vaccination and potentially reducing vaccine hesitancy,” Bianchi added.

The COVID vaccine trials did not specifically ask participants whether they saw adverse side effects in their menstrual cycles or volumes — an omission Bianchi attributes to the fact “the Emergency Use Authorization was really focused on critical safety issues” and “changes to your menstrual cycle is really not a life and death issue.”

The new studies will build on existing research and leverage data from menstrual tracking applications to evaluate the potential impacts of COVID vaccination on menstrual health among geographically and racially and ethnically diverse populations.