A latest evaluation of reports from greater than 35,000 people offers probably the most comprehensive assessment thus far of menstrual changes experienced by pre- and post-menopausal individuals in the primary two weeks after receiving the COVID-19 vaccine. Published within the journal Science Advances, the study adds to the evidence that significant numbers of individuals experience this unexpected side effect.

“Menstruating and formerly menstruating people began sharing that they experienced unexpected bleeding after being administered a COVID-19 vaccine in early 2021,” the scientists who led the study wrote. Because vaccine trials typically don’t ask about menstrual cycles or bleeding, this side effect was largely ignored or dismissed.

Doctors who weighed in on the topic after hearing early reports about post-vaccination menstrual changes were often dismissive of patients’ concerns, said Kathryn Clancy, a professor of anthropology on the University of Illinois Urbana-Champaign who led the research with Katharine Lee, an anthropology professor at Tulane University. Some clinicians said it was unclear how a vaccine could trigger such changes.

Nonetheless, other vaccines – including those for typhoid, Hepatitis B and HPV – are sometimes related to changes in menstruation, Clancy said. These unwanted effects are believed to be tied to an uptick in immune-related inflammatory pathways and are less prone to be driven by hormonal changes.

“We suspect that for most individuals the changes related to COVID-19 vaccination are short-term, and we encourage anyone who’s nervous to contact their doctor for further care,” Lee said. “We would like to reiterate that getting the vaccine is the most effective ways to stop getting very sick with COVID, and we all know that having COVID itself can lead not only to changes in periods, but additionally hospitalization, long COVID and death.”

The researchers used a survey to question people about their experiences after vaccination. Launched in April 2021, the survey asked for demographic and other information but focused on respondents’ reproductive history and experiences regarding menstrual bleeding. The team downloaded the information from the surveys on June 29, 2021. Only those that had not been diagnosed with COVID-19 were included within the evaluation, as COVID-19 itself is usually related to menstrual changes. The study also excluded data from people 45 to 55 years old to avoid confounding the outcomes by including menstrual changes related to perimenopause.

We focused our evaluation on those that usually menstruate and people who don’t currently menstruate but have prior to now. The latter group included postmenopausal individuals and people on hormonal therapies that suppress menstruation, for whom bleeding is very surprising.”

Kathryn Clancy, professor of anthropology, University of Illinois Urbana-Champaign

A statistical evaluation revealed that 42.1% of menstruating survey respondents reported a heavier menstrual flow after receiving the COVID-19 vaccine. Some experienced this in the primary seven days but many others saw changes 8-14 days after vaccination. Roughly the identical proportion, 43.6%, reported no alteration of their menstrual flow after the vaccine, and a smaller percentage, 14.3%, saw a combination of no change or lighter flow, the researchers report.

Since the study relied on self-reported experiences logged greater than 14 days after vaccination, it cannot establish causality or be seen as predictive of individuals in the final population, Lee said. But it may point to potential associations between an individual’s reproductive history, hormonal status, demographics and changes in menstruation following COVID-19 vaccination.

For instance, the evaluation revealed that respondents who had experienced a pregnancy were almost certainly to report heavier bleeding after vaccination, with a slight increase amongst those that had not given birth. A majority of non-menstruating premenopausal respondents on hormonal treatment experienced breakthrough bleeding after receiving the vaccine. Greater than 70% of respondents using long-acting reversible contraception and 38.5% of those undergoing gender-affirming hormone treatments reported this side effect.

Participants who classified themselves as non-white, Hispanic/Latinx, or who were older, and people who experienced fever or fatigue as a side effect of vaccination were more likely than other groups to report heavier menstrual flow after vaccination. Those that had experienced endometriosis, menorrhagia, fibroids or other reproductive problems also were more prone to report a heavier menstrual flow post-vaccination, the team found.

While the uptick in menstrual flow for some people could also be transitory and quickly resolve, unexpected changes in menstruation can still cause concern, Lee said.

“Unexpected breakthrough bleeding is one among the early signs of some cancers in post-menopausal people and in those that use gender-affirming hormones, so experiencing it may make people worry and require expensive and invasive cancer-screening procedures,” Lee said.

“This screening could be very vital so we are able to catch cancers early,” Clancy said. “Anyone with breakthrough bleeding should see their doctor. For diagnostic purposes, it will be helpful to know whether there are other causes for the bleeding.”

“We might like to see future vaccine testing protocols incorporate questions on menstruation that transcend screening for pregnancy,” Lee said. “Menstruation is an everyday process that responds to every kind of immune and energetic stressors, and folks notice changes to their bleeding patterns, yet we do not are inclined to speak about it publicly.”

Clancy is an affiliate of the Beckman Institute for Advanced Science and Technology, the Carle R. Woese Institute for Genomic Biology and the Center for Social and Behavioral Science on the U. of I. Lee is also an affiliate of the U. of I. anthropology department and the CSBS.

The Beckman Institute, the CSBS and the Interdisciplinary Health Sciences Institute at Illinois supported this research, as did the National Institutes of Health, the Foundation for Barnes-Jewish Hospital in St. Louis and the Siteman Cancer Center in St. Louis.

Source:

University of Illinois at Urbana-Champaign

Journal reference:

Lee, K.M.N., et al. (2022) Investigating trends in those that experience menstrual bleeding changes after SARS-CoV-2 vaccination. Science Advances. doi.org/10.1126/sciadv.abm7201.