Do COVID Vaccines Affect Your Period & Menstrual Cycle?
- There have been anecdotal reports of COVID-19 vaccines affecting menstrual cycles
- While we don’t know for sure whether COVID-19 vaccines are causing these changes, experts believe it’s plausible
- Changes potentially caused by the vaccine should be temporary, lasting only one menstrual cycle, and should not impact fertility
Many women are reporting weird menstrual cycles after vaccination, some with late periods, and others with lighter or heavier flows than normal. And even some post-menopausal women and those taking period-preventing hormones are reporting a sudden return of menstrual bleeding after vaccination.
These claims drew the attention of Dr. Kate Clancy, an associate professor of Anthropology at the University of Illinois, when she experienced a heavier than normal period herself. “I’m a week and a half out from dose 1 of Moderna, got my period maybe a day or so early, and am gushing like I’m in my 20s again,” she tweeted.
Intrigued, she and her colleague Katharine Lee, a postdoctoral scholar of public health sciences at Washington University, decided to investigate. They are collecting data on menstrual changes after vaccination through a detailed online survey.
Clancy’s study is still ongoing, but she recently told Salon that her early data show that “people who have historically menstruated, but are not menstruating now because they are, for instance, trans on gender-affirming hormones, on long-acting reversible contraception, or are postmenopausal… some number of them have experienced bleeding when they had not for a very long period of time.”
For “people who expected to menstruate,” she added, report either “no change,” “absent or late,” or “heavy and early” periods.
Is COVID Vaccination Really Causing These Changes?
The short answer is we do not know whether vaccination is affecting women’s menstrual cycles, and we are unlikely to get any firm answers soon.
“The variability of the menstrual cycle, even within one woman, is quite large in general,” Jerilynn Prior, a professor of endocrinology at the University of British Columbia told CBC news. And because so many women experience irregular periods, it’s impossible to tell whether the reported changes are due to vaccination, or would have occurred regardless.
But could vaccination affect your menstrual cycle? Certainly. There are a few ways vaccination might plausibly affect a woman’s menstruation, according to Dr. Jen Gunter, a gynecologist and author of the Vagina Bible.
First, vaccination could indirectly affect your period, by altering your stress levels. Perhaps you’re worried about potential vaccine side effects like fatigue, chills, and headaches. Or perhaps your stress levels drop because you’re so relieved to finally get vaccinated.
Mental and physical stressors like long work hours and illness can definitely affect your period—typically by causing it to come later than expected. In fact, one study found about a quarter of menstruating women with COVID reported cycle changes, mostly delayed cycles and lighter periods. (Reassuringly, the study also looked at fertility-related hormones, and no changes were seen.)
Another possibility is a direct effect, in which your body’s immune response to the vaccine, which involves inflammation, also affects the uterine lining (endometrium). The endometrium contains many immune cells, and inflammatory signals involving those cells help trigger the normal shedding of the endometrium during menstruation.
But even if period changes are—indirectly or directly—triggered by vaccination, the effects should be temporary, lasting only one menstrual cycle.
When Should You Seek Medical Attention or Treatment?
Because any mild menstrual changes after vaccination are likely minor and temporary, you do not need to seek medical attention if your period is slightly heavier or lighter than normal, or later or earlier than normal, or if you experience light spotting.
That said, absolutely do not ignore the types of bleeding that would normally lead you to seek medical attention. “You should talk to your doctor right away if you’re pregnant and experiencing abnormal bleeding, or hemorrhaging or experiencing incredibly heavy bleeding, or post-menopausal and bleeding,” advises Dr. Margaret Polaneczky, a gynecologist at Weill Cornell Medicine in New York.
Do Menstrual Cycle Changes Imply That the Vaccines Will Harm My Pregnancy or Fertility?
Reports of menstrual changes, associated with the vaccines or not, have made some women understandably skittish about whether the vaccines might affect their pregnancies or chances of conceiving. Misinformation circulating on social media claiming that vaccines or “vaccine-induced shedding” will harm women’s pregnancies or fertility can heighten these concerns.
Fortunately, “there is no evidence that the vaccine can lead to loss of fertility. While fertility was not specifically studied in the clinical trials of the vaccine, no loss of fertility has been reported among trial participants or among the millions who have received the vaccines since their authorization, and no signs of infertility appeared in animal studies,” according to The American College of Obstetricians and Gynecologists (ACOG).
Moreover, although we don’t have much direct data from the early vaccine trials, what we do have is reassuring. In the phase 3 trial of the Pfizer-BioNTech COVID vaccine, 23 women conceived during the course of the trial, 11 in the placebo group and 12 in the vaccine group. Two of these women reported adverse events, but both were in the placebo group.
A recent observational study of women who got vaccinated while pregnant similarly found no signs of elevated rates of pregnancy-related complications or congenital abnormalities.
By contrast, pregnant women are at an elevated risk of severe COVID, being hospitalized and needing mechanical ventilation, compared to other women their age. They also appear to have an elevated risk of preterm delivery.
Should I Still Get Vaccinated if I Am Undergoing IVF or Another Fertility-Related Procedure?
“Patients undergoing fertility treatment and pregnant patients” should receive the vaccine, according to the American Society of Reproductive Medicine. “Since the vaccine is not a live virus, there is no reason to delay pregnancy attempts because of vaccination administration or to defer treatment until the second dose has been administered.”
They do, however, make one caveat to this recommendation: Women scheduled for “elective surgery or outpatient procedures, including oocyte retrieval, embryo transfer, and intrauterine insemination, [should] avoid COVID-19 vaccination at least three days prior and three days after their procedure.” This is not because vaccination would interfere with your procedure’s likelihood of success, but because side effects from vaccination such as fever could make pre- and post-procedure monitoring for infections more challenging.
What Claims About Menstrual Changes Really Tell Us: Inclusion in Clinical Trials is Not Enough
The reported menstrual changes are not cause for concern, but they are definitely cause for frustration. The unfortunate truth is that we don’t know, and won’t know, whether COVID vaccination causes temporary changes in menstrual cycles, because no one asked about women’s cycles in the vaccine trials.
Until the 1990s, clinical trials used to exclude women as a matter of course. Thankfully, women’s inclusion in clinical trials for treatments to be used in both sexes is mandatory. This is undoubtedly a better state of affairs, but inclusion alone is still not sufficient. As Clancy told Salon. “It’s not enough to include [women] if you don’t consider their particular community needs, or their particular differences that make their inclusion necessary.”
As Dr. Guntner wrote in her substack newsletter: “The lack of data regarding menstrual cycles and vaccines is infuriating. I am not concerned about downstream effects regarding infertility or recurrent miscarriages as this has been well-studied for a variety of vaccines. But knowing about menstrual irregularity is as important as knowing about fever.”
Medical Experts Continue to Assert that COVID Vaccines Do Not Impact Fertility. The American College of Obstetricians and Gynecologists (ACOG), the American Society for Reproductive Medicine (ASRM), and the Society for Maternal-Fetal Medicine (SMFM). 2021