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Thousands of women report that COVID-19 vaccines affect their period. AnanR2107/Getty Images
  • COVID-19 vaccines can cause several side effects, which are mostly mild.
  • However, changes to menstrual cycles or unexpected vaginal bleeding are not among the listed side effects for any COVID-19 vaccines available in the United Kingdom or the United States.
  • Despite this, thousands of women reported period changes following vaccination to the U.K.’s Medicines and Healthcare Products Regulatory Agency (MHRA).
  • Researchers have not established a formal link between the vaccines and menstrual cycle changes, and some medical professionals want to study the possibility.

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Globally, more than 4.6 million people have died due to COVID-19. Vaccines are a crucial component in reducing the spread of the virus.

Some researchers wonder what side effects these life-saving vaccines might have on women’s menstrual cycles.

In an editorial in theBMJ, Dr. Victoria Male calls for further investigation into these vaccines’ potential effects on menstrual health. Dr. Male is a reproductive specialist at Imperial College London in London, U.K.

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In the early days of the pandemic, the best way to prevent contracting and spreading the virus was to wear masks and practice social distancing. Doctors still recommend these same practices alongside getting one of the approved COVID-19 vaccines.

The Moderna, AstraZeneca, Pfizer–BioNTech, and Jonson and Johnson’s Janssen vaccines are currently available in the U.K.

The Moderna, Pfizer, and Janssen vaccines are also available in the U.S.

According to the Centers for Disease Control and Prevention (CDC), some of the common side effects of the vaccines include:

  • pain at the site of vaccination
  • tiredness
  • fatigue
  • fever

To date, none of the COVID-19 vaccine manufacturers list any issues pertinent to menstrual health as a side effect.

However, Dr. Male says more than 30,000 people reported menstrual cycle changes following vaccination to the MHRA. She explains that most people who report experiencing changes to their menstrual cycle say things typically return to normal by the next cycle. Importantly, there is no evidence that COVID-19 vaccination adversely affects fertility.

The author says that research is needed to determine a definitive link between the two and what is triggering that response in some people.

“If there is a connection, it is likely to be a result of the immune response to vaccination rather than a specific vaccine component,” Dr. Male writes.

Stress can disrupt the menstrual cycle and cause cycles to vary or even stop altogether. The immune response created by vaccines can cause this type of stress reaction.

According to Dr. Male, the lack of research on the effects of COVID-19 vaccines on periods is due to the relatively low occurrence of these reports.

Even if menstrual cycle changes occur infrequently, it is still important to fully explore the possible effects that the COVID-19 vaccines may have.

“Vaccine hesitancy among young women is largely driven by false claims that COVID-19 vaccines could harm their chances of future pregnancy,” Dr. Male writes. “Failing to thoroughly investigate reports of menstrual changes after vaccination is likely to fuel these fears.”

Dr. Katharine Lee, a postdoctoral research scholar in the Division of Public Health Sciences at Washington University School of Medicine in St. Louis, MO, weighed in on the importance of beginning this research.

“I am happy to see this paper published because it is an important area of research,” Dr. Lee told Medical News Today.

“Variation in menstrual cycles is surprisingly understudied, even though we know that they should respond to lots of kinds of stressors, including immune and inflammatory responses. Dr. Male makes a number of good points, and I’m especially glad she’s highlighting the safety of the vaccines,” said Dr. Lee.

MNT also spoke with Dr. Sarah Gray — a general practitioner based in Cornwall, England. Dr. Gray is an expert in women’s health and ran a specialist women’s health clinic for the National Health Service (NHS) for 15 years.

Dr. Gray said, “The control of menstrual bleeding is complex with potential effects from the brain, ovaries, and uterus itself. It is plausible that the effects of either [SARS-CoV-2] infection or vaccination on the immune system could affect this control pathway, and any research would be greatly valued.”

“Women’s health has not been a research priority for the last 20 years and there is much we do not know,” she added.

MNT also interviewed Dr. Kathryn Clancy, who is “glad to see this publication and agrees with Dr. Male’s point of view that these changes are real and worth exploring more deeply.”

Dr. Clancy is an assistant professor at the University of Illinois at Urbana-Champaign in Champaign, IL. She says she is involved in similar research.

“Our work proposes similar biological mechanisms for this relationship between acute immune activation and menstrual repair mechanisms,” said Dr. Clancy. She added:

“I am dismayed that the research design of vaccine trials makes it impossible at this time to actually explore this relationship and hope drug and vaccine manufacturers in the future take these considerations into account.”

This article was published in September 2021. In January 2022, a large study set out to investigate the affect of COVID-19 vaccines on menstrual cycles.

The researchers found only small, temporary increases in cycle length that were not clinically significant. Read more about that study and its limitations here.

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