Even People Who No Longer Menstruate Saw COVID Vaccine-Related Period Symptoms, Research Shows

The new findings “underscore the importance of including gender-diverse people” in research.

Hand holding vaccine with menstrual pad on background and red circles
Photo: Alex Sandoval

Even people who don't typically menstruate—including transgender people, people on long-acting contraceptives, and post-menopausal women—have experienced menstrual changes and unexpected bleeding after receiving a COVID-19 vaccine, new preliminary research shows.

The new study, published on preprint server MedRxiv, sought to expand on existing research of the effects of COVID-19 vaccines on menstrual cycles, which until now focused primarily on cisgender women who menstruate.

"It's important to examine the impacts of COVID-19 vaccination on menstruation and breakthrough bleeding in people who are not [cisgender] women because they are too often left out of the discussion," first study author Katharine Lee, PhD, a postdoctoral research scholar in the division of public health sciences at Washington University, said in a press release. "I hope that this study adds to the increasing evidence that maybe we should include periods as part of vaccine research more broadly. Our findings also underscore the importance of including gender-diverse people when we study parts of biology that are closely linked with sex-based reproductive physiology like periods."

Formerly Menstruating People and Unexpected Bleeding

The new research, conducted by scientists at the University of Illinois at Urbana-Champaign and Washington University St. Louis School of Medicine, aimed to take a broader look at who experienced menstrual changes following COVID-19 vaccination.

To do this, the research team distributed an online survey about post-vaccination menstrual experiences to 160,000 people between the ages of 18 and 80. All of the participants were fully vaccinated and, to the best of their knowledge, had not contracted COVID-19. The participants were asked to share details about their menstrual cycles along with their gender identity. Of the 39,129 participants who responded to the survey, 35,572 identified as women, while 3,557 identified as gender diverse.

Among people who were menstruating regularly at the time of the survey, 56% reported experiencing irregular menstrual symptoms; most commonly heavier bleeding.

Non-menstruating people were split into two groups: premenopausal people (individuals using long-acting reversible contraceptives and/or gender-affirming treatment that suppresses menstruation) and post-menopausal people over the age of 55 who had not menstruated in over a year prior to COVID-19 vaccination.

Of the people not menstruating due to gender-affirming hormones, 39% experienced breakthrough bleeding; 71% of people on long-acting contraceptives also experienced breakthrough bleeding. Some also experienced chest or breast soreness (9%) and 46% experienced other symptoms common with menstruation, like cramping and bloating. Among post-menopausal people, 66% experienced unexpected bleeding, despite not having menstruated for an extended period of time.

It's also worth noting that some demographics were more likely to experience changes to menstruation than others: Those who were older, Hispanic, had been diagnosed with a reproductive condition (like endometriosis, fibroids, or PCOS), used hormonal contraception, or previously had been pregnant were more likely to experience heavier periods. In addition, people who experienced more side effects after the shots—like fever or fatigue—had a greater chance of experiencing menstrual changes, as well.

Inflammation, Blood Flow Changes May Disrupt Menstruation

It's well known that menstruation and bleeding are influenced by both external and internal stressors, study authors said. Stress and illness, changes in nutrition and exercise, weight loss and gain, pregnancy, and miscarriage are all known to change people's typical pattens of menstruation.

So it's not surprising that the stress that comes with vaccination and the side effects resulting from the body's immune response may alter menstrual symptoms, according to Hugh Taylor, MD, chair of obstetrics, gynecology, and reproduction sciences at the Yale School of Medicine and Yale Medicine.

Vaccination triggers an inflammatory response along with body-wide effects on blood flow. This inflammation is believed to reach various organs, such as the uterus, and may therefore potentially disrupt how the body sheds and rebuilds the uterine lining during and after menstruation. "Mostly—it is important to say—we just don't exactly know why," Michelle Forcier, MD, MPH, a clinician with FOLX Health specializing in gender-affirming care, told Health.

And it seems the COVID-19 vaccine isn't the first to affect menstrual cycles: Past evidence found a link between the typhoid vaccine and menstrual irregularities, and menstrual changes have been recorded in people who received the hepatitis B vaccine and the HPV vaccine. The menstrual changes from any vaccine—including the COVID-19 vaccine—are short-lived and appear to have no impact on future fertility. "Several studies have shown no effect on female fertility, no pregnancy complications and no increased risk of miscarriage," Dr. Taylor said.

COVID, on the other hand, can cause serious damage and be life-threatening. Additionally, many people with long COVID have reported long-lasting irregularities in their menstrual cycles, including unusual clots, and delayed or skipped periods. "We cannot emphasize enough the advantages of COVID vaccination. Because the benefits clearly outweigh any minor side effects, we highly recommend getting the COVID vaccine and boosters," Dr. Taylor said.

Harms of Unexpected Bleeding

Many people—especially transgender men, trans-masculine, and nonbinary individuals—find menstrual bleeding physically and psychologically intolerable, Dr. Forcier said, adding that it can exacerbate gender dysphoria, or feelings of discomfort or distress due to a mismatched gender identity and sex assigned at birth.

"For a person who has significant menses dysphoria and had to go through some bleeding post COVID vaccination, the first response is listening acknowledging their experience and pain," Dr. Forcier said.

Study authors also recognized the potential for physical harm for people managing menstruation in public, like gender-diverse people who must navigate public restrooms.

Certain harms exist for post-menopausal people who experience unexpected bleeding, too: According to study authors, breakthrough bleeding in formerly menstruating people can be a sign of cancer, and can lead to "unnecessary, painful, and expensive diagnostic procedures."

In recognizing that this breakthrough bleeding can occur in various populations, health care providers can help people make careful, informed decisions about their health, and prepare vaccine recipients for the potential side effects and create a more tolerable experience in the event of breakthrough bleeding or menstrual-related symptoms after being vaccinated for COVID-19.

Overall, health experts hope the new research will soon be peer-reviewed so that health care providers can utilize them to counsel patients who are gender-diverse. "The more medical and public health persons can demonstrate what we know, what we don't know, and what we are doing to figure things out," Dr. Forcier said, "the better conversations people can have as they decide what is best for their health and individual needs."

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