Survey suggests SARS-CoV-2 vaccination may alter menses, cause breakthrough bleeding
In a recent survey, 42% of women said they experienced heavier menstrual bleeding following SARS-CoV-2 vaccination.
Results also showed that a majority of non-menstruating, premenopausal women taking hormonal treatments experienced breakthrough bleeding after vaccination.
Researchers said this possible side effect was likely missed in clinical trials, which did not assess menstrual cycles or bleeding. Analyses of the survey data, which were published in Science Advances, revealed certain characteristics were associated with changes in menstruation.
“This is the very first characterization of postvaccine menstrual bleeding changes for a gender-diverse sample of pre- and postmenopausal people,” Katharine M. N. Lee, PhD, MS, a postdoctoral research fellow in the division of public health sciences at Washington University in St. Louis in Missouri, and colleagues wrote. “We cannot estimate prevalence or incidence based on our methodological approach of this emergent phenomenon, and the associations reported here cannot establish causality. However, the trends we observe support hypothesis development for additional prospective studies in hemostatic and inflammatory changes to the endometrium after an acute immune response.”
Lee and colleagues initially launched the web-based survey through social media on April 7, 2021, to collect data on participants’ typical menstrual experiences, menstrual experiences following vaccination, reproductive history, hormonal treatments and menstruation-related diagnoses. According to the researchers, the survey was picked up by news outlets and in online web searches, so “the data collected by this survey represent[ed] extensive snowball sampling via many channels” by the time they downloaded their preliminary results on June 29, 2021.
After eliminating duplicate, incomplete and inappropriate responses, as well responses from participants aged younger than 18 years, those who did not complete their vaccine series and those who had COVID-19, Lee and colleagues assessed 39,129 participants for general data analyses. Among these, the researchers analyzed menstrual changes in 35,660 participants who had completed a two-dose vaccine regimen.
Changes in menstruating participants
Overall, 42.1% of regularly menstruating participants reported heavier menses than normal following their vaccination, 43.6% reported no changes and 14.3% reported a menstrual flow that was “not heavier,” meaning a mix of lighter or no change. Heavier menses was associated with non-white race, “Latinx” (a gender-inclusive term for people of Latin American descent) or Hispanic ethnicity, older age, having a reproductive condition, using hormonal contraception, having a previous pregnancy, having given birth and experiencing fever or fatigue after vaccination.
Additional analyses of reproductive conditions revealed that a greater proportion of respondents who had endometriosis (51.1%), menorrhagia (44.3%), fibroids (49.1%), polycystic ovarian syndrome (46.2%) and adenomyosis (54.9%) had a heavier menstrual flow compared with respondents who did not have reproductive conditions (40.9%).
Changes in non-menstruating participants
The researchers also analyzed menstrual changes in non-menstruating participants — which included premenopausal people using long-acting reversible contraceptives (LARCs), hormonal contraceptives and/or gender-affirming treatment, as well as postmenopausal people.
Among premenopausal participants who used hormonal treatments, 65.7% experienced breakthrough bleeding. Specifically, 70.5% of participants using LARC only and 38.5% of those using gender-affirming treatment had breakthrough bleeding.
In the non-menstruating premenopausal group, breakthrough bleeding was associated with Hispanic or “Latinx” ethnicity, having been pregnant but not given birth, having a reproductive condition, using LARC only and experiencing fever following vaccination.
Among postmenopausal participants, 66% experienced breakthrough bleeding. A greater proportion of those who had breakthrough bleeding vs. those who did not were younger and of Hispanic or “Latinx” ethnicity.
“The nature of this survey means that we cannot compare the incidence of different experiences here with the general population (meaning, 40% of this sample having an experience does not mean that is the rate of that experience out in the world),” Lee and colleagues cautioned. “The associations described here are not causal but provide evidence to better study these trends further. We emphasize that menstrual bleeding changes of this nature are generally not indicative of changes to fertility.”
Perspective
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This research plays a critically important role in highlighting the experience of the public around COVID-19 vaccine and menstruation. Menstrual cycles are inherently variable — for some individuals that can be negligible, and for others, they always vary a lot. We know that “stressors” such as fevers or illness can cause temporary changes to someone’s menstrual cycle, and for some individuals with stress-sensitive menstrual systems, that may be a slightly bigger or longer temporary change. Overall, the research is pointing to no or temporary small changes to a menstrual cycle with vaccination. If you experience something concerning to you, we always encourage you to check in with your health care provider.
The impact of vaccine hesitancy cannot be underestimated in public health. If reports of changes are being ignored or dismissed — such as what happened during vaccine rollout — then that creates greater mistrust and fuels fear. We need to do a better job of listening and validating the patient experience and work toward identifying issues important to the public — such as menstrual health — that we can integrate into future vaccine trials. Then, we can provide information on what to expect that helps to mitigate fears and concerns.
Menstrual health has been woefully understudied, not just in vaccine trials but in almost every area of research. The public has spoken: This is important to them. That should not be surprising. Half the population will, does and has menstruated. It is a routine biological function that has significance for both the individual and science. I hope we can learn from this for ongoing and future vaccine trials.
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