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Researchers have recently been looking at COVID-19 vaccines’ possible impact on periods. Stringer/Anadolu Agency via Getty Images
  • The impact of the COVID-19 vaccine on menstruation was not measured during any of the clinical trials but now studies are looking into people’s reports to see if there is a link.
  • A recent study has linked the COVID-19 vaccine to heavier menstrual flow and unexpected vaginal bleeding in some individuals.
  • Reports of changes to the menstrual cycle indicate they are temporary and short-lived, but women and people who menstruate or have menstruated need reliable information to make informed choices, and hopefully, combat vaccine hesitancy.

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There have been tens of thousands of reports of changes to menstrual cycles worldwide following COVID-19 vaccination, but a link has not yet been proven or disproven.

This is partly due to the failure of pharmaceutical companies to include questions about menstruation in their trials to date.

Dr. Viki Male, a lecturer in reproductive immunology at Imperial College London in the United Kingdom, designed vaccine protocols for clinical trials of the Ebola vaccine. She explained why not capturing data on menstruation during the COVID-19 vaccine trials was a missed opportunity in an email to Medical News Today:

“Because clinical trials are double-blinded, even the very simple question ‘Did you notice any change to your menstrual bleeding, or experience any unexpected vaginal bleeding?’ would have been extremely powerful: the control group means we would have a good idea of the background rate of these changes in the relevant population and the fact that it is blinded means that people’s expectations of seeing a change would not have affected reports. In the future, I hope a simple question like this will be included routinely.”

“Research into whether and how [COVID-19] vaccination affects menstrual periods and breakthrough bleeding has been playing catch up since this information was not collected during the trials.”
— Dr. Viki Male

The first study to be published using funding from the National Institutes of Health to investigate a link was published in January 2022 and showed vaccination could affect cycle but not menses length.

Now, a new study has looked not only at menstrual flow changes in those with a regular menstrual cycle but also at unexpected vaginal bleeding in people who previously menstruated but don’t any longer due to using hormonal contraception, menopause, or gender affirmative hormonal treatment.

To investigate whether or not there was a link between changes in menstruation or unexpected vaginal bleeding after vaccination, a team led by Dr. Kathryn Clancy from the University of Illinois at Urbana-Champaign, Champaign, IL designed a survey for vaccinated people who had not had COVID-19 and collected data on people’s ethnic identity, gender identity, age, and vaccination received.

First lead author Dr. Katharine Lee, a postdoctoral research scholar at Washington University in St. Louis, M.O. told MNT in an interview that they did not want to delay the vaccinations of the participants.

“We chose to do this study design because we are very pro-vaccine. So, we did not want to try to enroll people who were vaccinated or were not vaccinated or tell people to wait to get vaccinated. We were like, as soon as you can get it, you should still definitely get vaccinated.”

“But what we did want to hear about was people’s experiences because of the variety of stories that came in when [Dr. Kathryn Clancy] tweeted about her period in February of last year.”
— Dr. Katharine Lee

The researchers shared the survey on Twitter and other social media platforms and then analyzed the data analyzed collected between April 7, 2021, and June 29, 2021. Nine out of 10 of the 39,129 participants identified as women, while one in 10 participants identified as gender diverse.

Participants were asked about their period flow and cycle length and medical history. They were then asked about their experiences of their menstrual cycle after the first and second dose of their COVID-19 vaccines.

Of the participants with a regular menstrual cycle, 42% reported they bled more heavily than usual, while 44% reported no change after being vaccinated.

Of the postmenopausal individuals responding to the survey, 66% reported breakthrough bleeding, alongside, 71% of people on long-acting reversible contraceptives and 39% of people on gender-affirming hormones.

Further analysis found respondents with gynecological conditions were more at risk of heavier bleeding after vaccination. Those who experienced fever and fatigue after vaccination had previously been pregnant or given birth or who normally had a light menstrual flow were also more likely to report heavier bleeding after COVID-19 vaccination.

Hispanic and Latinx respondents were more likely than any other ethnic group to report heavier bleeding after vaccination if they had a regular menstrual cycle and to report breakthrough bleeding if they were postmenopausal.

Including participants recruited after vaccination could present some bias, as people were more likely to take part in a study if they think they have been affected said Dr. Male in an email.

“We can’t use this study to determine how common it is to experience a change to flow following vaccination because people who experienced a change are more likely to complete the survey, but we can look for patterns that might give us an idea of who is more at risk of experiencing changes,” she said.

Dr. Clancy told MNT that the purpose of the project was never to assess prevalence as only a prospective study can do that. She said they tried to draw attention to the problems people were experiencing after being met with disbelief and unfair treatment.

Dr. Clancy said they aimed to “[t]ry and collect these experiences and understand them better, and give patients an actual voice in this phenomenon that they have somewhere they can share what’s going on.”