STUDY: Some Women’s Menstruation Changes After COVID-19 Vaccination


Kay Smythe News and Commentary Writer
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A study published Friday in Science Advances reported that 42% of respondents had heavier cycles after receiving the COVID-19 vaccine.

Manufacturers of vaccines typically do not study how women’s menstrual cycles and bleeding occur post-vaccination, despite “many people” allegedly claiming they “experienced unexpected menstrual bleeding” after receiving the COVID-19 vaccination, the researchers of the study argued. Therefore, the researchers used self-reported data from a sample of almost 40,000 females across various demographics and sub-demographics to assess the extent to which they’d experienced similar symptoms.

Forty-two percent of respondents said they’d bled more heavily than they’d typically expect, 44% reported no changes, while a high number of non-menstruating women allegedly experienced breakthrough bleeding, according to the results. Most noticed a change within a week of receiving their first and second doses, the authors reported.

A majority of the respondents had received the Pfizer vaccine (21,620) or Moderna (13,001), the study continued. Others received Johnson & Johnson, Novavax, and “other” vaccines, the researchers claimed.

“Dr. Lee and I had our own wonky period experiences post-vaccine,” study author Dr. Kathryn Clancy said of her and her colleague, Dr. Katharine Lee, according to Technology Networks, “If Dr. Lee hadn’t pointed them out to me first, I may never have made the connection myself. After I tweeted about it and the response was overwhelming, we designed a survey instrument that would allow us to capture these experiences as well as any factors that might make one more at risk of this side effect. We really wanted to listen to people and validate their concerns because there were so many who were quick to dismiss them.”

“Our key finding is that increased bleeding (heavier among menstruating people, and breakthrough bleeding among non-menstruating people) is real, mechanistically plausible and experienced by a significant number of people,” Clancy continued, Technology Networks reported, “It is also now supported by several prospective studies that have also found the same thing.” (RELATED: Hailey Bieber Hospitalized With Brain Issues, Potentially COVID-Related)

The CDC announced in 2021 that they were doing “exploratory work” to decide whether there would be a study into COVID-19 and menstrual bleeding irregularities. Shortly after, they announced a study into abnormal uterine bleeding diagnosis after COVID-19 vaccination, according to a release on their website, and their results were similar to that of Clancy’s research.