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Many women who got a COVID-19 vaccine have reported heavier bleeding during their periods since they had the shots.
A team of researchers investigated the trend and set out to find out who among the vaccinated were more likely to experience the menstruation changes.
The researchers were led by Katharine M.N. Lee, PhD, MS, of the division of public health sciences at Washington University in St. Louis. Their findings were published ahead of print in Science Advances.
The investigators analyzed more than 139,000 responses from an online survey from both currently and formerly menstruating women.
They found that, among people who have regular periods, about the same percentage had heavier bleeding after they got a COVID vaccine as had no change in bleeding after the vaccine (44% vs. 42%, respectively).
“A much smaller portion had lighter periods,” they write.
The phenomenon has been difficult to study because questions about changes in menstruation are not a standard part of vaccine trials.
Date of last period is often tracked in clinical trials to make sure a participant is not pregnant, but the questions about periods often stop there.
Additionally, periods are different for everyone and can be influenced by all sorts of environmental factors, so making associations regarding exposures is problematic.
No changes found to fertility
The authors emphasized that, generally, changes to menstrual bleeding are not uncommon nor dangerous. They also emphasized that the changes in bleeding don’t mean changes to fertility.
The uterine reproductive system is flexible when the body is under stress, they note.
“We know that running a marathon may influence hormone concentrations in the short term while not rendering that person infertile,” the authors write.
However, they acknowledge that investigating these reports is critical in building trust in medicine.
This report includes information that hasn’t been available through the clinical trial follow-up process.
For instance, the authors write, “To the best of our knowledge, our work is the first to examine breakthrough bleeding after vaccination in either pre- or postmenopausal people.”
Reports of changes to periods after vaccination started emerging in 2021. But without data, reports were largely dismissed, fueling criticism from those waging campaigns against COVID vaccines.
Dr. Lee and colleagues gathered data from those who responded to the online survey and detailed some trends.
People who were bleeding more heavily after vaccination were more likely to be older, Hispanic, had vaccine side effects of fever and fatigue, had been pregnant at some point, or had given birth.
People with regular periods who had endometriosis, prolonged bleeding during their periods, polycystic ovarian syndrome (PCOS) or fibroids were also more likely to have increased bleeding after a COVID vaccine.
Breakthrough bleeding
For people who don’t menstruate, but have not reached menopause, breakthrough bleeding happened more often in women who had been pregnant and/or had given birth.
Among respondents who were postmenopausal, breakthrough bleeding happened more often in younger people and/or those who are Hispanic.
More than a third of the respondents (39%) who use gender-affirming hormones that eliminate menstruation reported breakthrough bleeding after vaccination.
The majority of premenopausal people on long-acting, reversible contraception (71%) and the majority of postmenopausal respondents (66%) had breakthrough bleeding as well.
The authors note that you can’t compare the percentages who report these experiences in the survey with the incidence of those who would experience changes in menstrual bleeding in the general population.
The nature of the online survey means it may be naturally biased because the people who responded may be more often those who noted some change in their own menstrual experiences, particularly if that involved discomfort, pain, or fear.
Researchers also acknowledge that Black, Indigenous, Latinx, and other respondents of color are underrepresented in this research and that represents a limitation in the work.
Alison Edelman, MD, MPH, with the department of obstetrics and gynecology at Oregon Health & Science University in Portland, was not involved with Dr. Lee and associates’ study but has also studied the relationship between COVID vaccines and menstruation.
Her team’s study found that COVID vaccination is associated with a small change in time between periods but not length of periods.
She said about the work by Dr. Lee and colleagues, “This work really elevates the voices of the public and what they’re experiencing.”
The association makes sense, Dr. Edelman says, in that the reproductive system and the immune system talk to each other and inflammation in the immune system is going to be noticed by the system governing periods.
Lack of data on the relationship between exposures and menstruation didn’t start with COVID. “There has been a signal in the population before with other vaccines that’s been dismissed,” she said.
Tracking menstruation information in clinical trials can help physicians counsel women on what may be coming with any vaccine and alleviate fears and vaccine hesitancy, Dr. Edelman explained. It can also help vaccine developers know what to include in information about their product.
“When you are counseled about what to expect, it’s not as scary. That provides trust in the system,” she said. She likened it to original lack of data on whether COVID-19 vaccines would affect pregnancy.
“We have great science now that COVID vaccine does not affect fertility and [vaccine] does not impact pregnancy.”
Another important aspect of this paper is that it included subgroups not studied before regarding menstruation and breakthrough bleeding, such as those taking gender-affirming hormones, she added.
Menstruation has been often overlooked as important in clinical trial exposures but Dr. Edelman hopes this recent attention and question will escalate and prompt more research.
“I’m hoping with the immense outpouring from the public about how important this is, that future studies will look at this a little bit better,” she says.
She said when the National Institutes of Health opened up funding for trials on COVID-19 vaccines and menstruation, researchers got flooded with requests from women to share their stories.
“As a researcher – I’ve been doing research for over 20 years – that’s not something that usually happens. I would love to have that happen for every research project.”
The authors and Dr. Edelman declare that they have no competing interests. This research was supported in part by the University of Illinois Beckman Institute for Advanced Science and Technology, the University of Illinois Interdisciplinary Health Sciences Institute, the National Institutes of Health, the Foundation for Barnes-Jewish Hospital, and the Siteman Cancer Center.
Many women who got a COVID-19 vaccine have reported heavier bleeding during their periods since they had the shots.
A team of researchers investigated the trend and set out to find out who among the vaccinated were more likely to experience the menstruation changes.
The researchers were led by Katharine M.N. Lee, PhD, MS, of the division of public health sciences at Washington University in St. Louis. Their findings were published ahead of print in Science Advances.
The investigators analyzed more than 139,000 responses from an online survey from both currently and formerly menstruating women.
They found that, among people who have regular periods, about the same percentage had heavier bleeding after they got a COVID vaccine as had no change in bleeding after the vaccine (44% vs. 42%, respectively).
“A much smaller portion had lighter periods,” they write.
The phenomenon has been difficult to study because questions about changes in menstruation are not a standard part of vaccine trials.
Date of last period is often tracked in clinical trials to make sure a participant is not pregnant, but the questions about periods often stop there.
Additionally, periods are different for everyone and can be influenced by all sorts of environmental factors, so making associations regarding exposures is problematic.
No changes found to fertility
The authors emphasized that, generally, changes to menstrual bleeding are not uncommon nor dangerous. They also emphasized that the changes in bleeding don’t mean changes to fertility.
The uterine reproductive system is flexible when the body is under stress, they note.
“We know that running a marathon may influence hormone concentrations in the short term while not rendering that person infertile,” the authors write.
However, they acknowledge that investigating these reports is critical in building trust in medicine.
This report includes information that hasn’t been available through the clinical trial follow-up process.
For instance, the authors write, “To the best of our knowledge, our work is the first to examine breakthrough bleeding after vaccination in either pre- or postmenopausal people.”
Reports of changes to periods after vaccination started emerging in 2021. But without data, reports were largely dismissed, fueling criticism from those waging campaigns against COVID vaccines.
Dr. Lee and colleagues gathered data from those who responded to the online survey and detailed some trends.
People who were bleeding more heavily after vaccination were more likely to be older, Hispanic, had vaccine side effects of fever and fatigue, had been pregnant at some point, or had given birth.
People with regular periods who had endometriosis, prolonged bleeding during their periods, polycystic ovarian syndrome (PCOS) or fibroids were also more likely to have increased bleeding after a COVID vaccine.
Breakthrough bleeding
For people who don’t menstruate, but have not reached menopause, breakthrough bleeding happened more often in women who had been pregnant and/or had given birth.
Among respondents who were postmenopausal, breakthrough bleeding happened more often in younger people and/or those who are Hispanic.
More than a third of the respondents (39%) who use gender-affirming hormones that eliminate menstruation reported breakthrough bleeding after vaccination.
The majority of premenopausal people on long-acting, reversible contraception (71%) and the majority of postmenopausal respondents (66%) had breakthrough bleeding as well.
The authors note that you can’t compare the percentages who report these experiences in the survey with the incidence of those who would experience changes in menstrual bleeding in the general population.
The nature of the online survey means it may be naturally biased because the people who responded may be more often those who noted some change in their own menstrual experiences, particularly if that involved discomfort, pain, or fear.
Researchers also acknowledge that Black, Indigenous, Latinx, and other respondents of color are underrepresented in this research and that represents a limitation in the work.
Alison Edelman, MD, MPH, with the department of obstetrics and gynecology at Oregon Health & Science University in Portland, was not involved with Dr. Lee and associates’ study but has also studied the relationship between COVID vaccines and menstruation.
Her team’s study found that COVID vaccination is associated with a small change in time between periods but not length of periods.
She said about the work by Dr. Lee and colleagues, “This work really elevates the voices of the public and what they’re experiencing.”
The association makes sense, Dr. Edelman says, in that the reproductive system and the immune system talk to each other and inflammation in the immune system is going to be noticed by the system governing periods.
Lack of data on the relationship between exposures and menstruation didn’t start with COVID. “There has been a signal in the population before with other vaccines that’s been dismissed,” she said.
Tracking menstruation information in clinical trials can help physicians counsel women on what may be coming with any vaccine and alleviate fears and vaccine hesitancy, Dr. Edelman explained. It can also help vaccine developers know what to include in information about their product.
“When you are counseled about what to expect, it’s not as scary. That provides trust in the system,” she said. She likened it to original lack of data on whether COVID-19 vaccines would affect pregnancy.
“We have great science now that COVID vaccine does not affect fertility and [vaccine] does not impact pregnancy.”
Another important aspect of this paper is that it included subgroups not studied before regarding menstruation and breakthrough bleeding, such as those taking gender-affirming hormones, she added.
Menstruation has been often overlooked as important in clinical trial exposures but Dr. Edelman hopes this recent attention and question will escalate and prompt more research.
“I’m hoping with the immense outpouring from the public about how important this is, that future studies will look at this a little bit better,” she says.
She said when the National Institutes of Health opened up funding for trials on COVID-19 vaccines and menstruation, researchers got flooded with requests from women to share their stories.
“As a researcher – I’ve been doing research for over 20 years – that’s not something that usually happens. I would love to have that happen for every research project.”
The authors and Dr. Edelman declare that they have no competing interests. This research was supported in part by the University of Illinois Beckman Institute for Advanced Science and Technology, the University of Illinois Interdisciplinary Health Sciences Institute, the National Institutes of Health, the Foundation for Barnes-Jewish Hospital, and the Siteman Cancer Center.
Many women who got a COVID-19 vaccine have reported heavier bleeding during their periods since they had the shots.
A team of researchers investigated the trend and set out to find out who among the vaccinated were more likely to experience the menstruation changes.
The researchers were led by Katharine M.N. Lee, PhD, MS, of the division of public health sciences at Washington University in St. Louis. Their findings were published ahead of print in Science Advances.
The investigators analyzed more than 139,000 responses from an online survey from both currently and formerly menstruating women.
They found that, among people who have regular periods, about the same percentage had heavier bleeding after they got a COVID vaccine as had no change in bleeding after the vaccine (44% vs. 42%, respectively).
“A much smaller portion had lighter periods,” they write.
The phenomenon has been difficult to study because questions about changes in menstruation are not a standard part of vaccine trials.
Date of last period is often tracked in clinical trials to make sure a participant is not pregnant, but the questions about periods often stop there.
Additionally, periods are different for everyone and can be influenced by all sorts of environmental factors, so making associations regarding exposures is problematic.
No changes found to fertility
The authors emphasized that, generally, changes to menstrual bleeding are not uncommon nor dangerous. They also emphasized that the changes in bleeding don’t mean changes to fertility.
The uterine reproductive system is flexible when the body is under stress, they note.
“We know that running a marathon may influence hormone concentrations in the short term while not rendering that person infertile,” the authors write.
However, they acknowledge that investigating these reports is critical in building trust in medicine.
This report includes information that hasn’t been available through the clinical trial follow-up process.
For instance, the authors write, “To the best of our knowledge, our work is the first to examine breakthrough bleeding after vaccination in either pre- or postmenopausal people.”
Reports of changes to periods after vaccination started emerging in 2021. But without data, reports were largely dismissed, fueling criticism from those waging campaigns against COVID vaccines.
Dr. Lee and colleagues gathered data from those who responded to the online survey and detailed some trends.
People who were bleeding more heavily after vaccination were more likely to be older, Hispanic, had vaccine side effects of fever and fatigue, had been pregnant at some point, or had given birth.
People with regular periods who had endometriosis, prolonged bleeding during their periods, polycystic ovarian syndrome (PCOS) or fibroids were also more likely to have increased bleeding after a COVID vaccine.
Breakthrough bleeding
For people who don’t menstruate, but have not reached menopause, breakthrough bleeding happened more often in women who had been pregnant and/or had given birth.
Among respondents who were postmenopausal, breakthrough bleeding happened more often in younger people and/or those who are Hispanic.
More than a third of the respondents (39%) who use gender-affirming hormones that eliminate menstruation reported breakthrough bleeding after vaccination.
The majority of premenopausal people on long-acting, reversible contraception (71%) and the majority of postmenopausal respondents (66%) had breakthrough bleeding as well.
The authors note that you can’t compare the percentages who report these experiences in the survey with the incidence of those who would experience changes in menstrual bleeding in the general population.
The nature of the online survey means it may be naturally biased because the people who responded may be more often those who noted some change in their own menstrual experiences, particularly if that involved discomfort, pain, or fear.
Researchers also acknowledge that Black, Indigenous, Latinx, and other respondents of color are underrepresented in this research and that represents a limitation in the work.
Alison Edelman, MD, MPH, with the department of obstetrics and gynecology at Oregon Health & Science University in Portland, was not involved with Dr. Lee and associates’ study but has also studied the relationship between COVID vaccines and menstruation.
Her team’s study found that COVID vaccination is associated with a small change in time between periods but not length of periods.
She said about the work by Dr. Lee and colleagues, “This work really elevates the voices of the public and what they’re experiencing.”
The association makes sense, Dr. Edelman says, in that the reproductive system and the immune system talk to each other and inflammation in the immune system is going to be noticed by the system governing periods.
Lack of data on the relationship between exposures and menstruation didn’t start with COVID. “There has been a signal in the population before with other vaccines that’s been dismissed,” she said.
Tracking menstruation information in clinical trials can help physicians counsel women on what may be coming with any vaccine and alleviate fears and vaccine hesitancy, Dr. Edelman explained. It can also help vaccine developers know what to include in information about their product.
“When you are counseled about what to expect, it’s not as scary. That provides trust in the system,” she said. She likened it to original lack of data on whether COVID-19 vaccines would affect pregnancy.
“We have great science now that COVID vaccine does not affect fertility and [vaccine] does not impact pregnancy.”
Another important aspect of this paper is that it included subgroups not studied before regarding menstruation and breakthrough bleeding, such as those taking gender-affirming hormones, she added.
Menstruation has been often overlooked as important in clinical trial exposures but Dr. Edelman hopes this recent attention and question will escalate and prompt more research.
“I’m hoping with the immense outpouring from the public about how important this is, that future studies will look at this a little bit better,” she says.
She said when the National Institutes of Health opened up funding for trials on COVID-19 vaccines and menstruation, researchers got flooded with requests from women to share their stories.
“As a researcher – I’ve been doing research for over 20 years – that’s not something that usually happens. I would love to have that happen for every research project.”
The authors and Dr. Edelman declare that they have no competing interests. This research was supported in part by the University of Illinois Beckman Institute for Advanced Science and Technology, the University of Illinois Interdisciplinary Health Sciences Institute, the National Institutes of Health, the Foundation for Barnes-Jewish Hospital, and the Siteman Cancer Center.
FROM SCIENCE ADVANCES