Nearly
half of the participants of a recent study who were menstruating
regularly at the time of the survey reported heavier bleeding during
their periods after receiving the COVID-19 vaccine. Others who did not
typically menstruate — including transgender men, people on long-acting
contraceptives and postmenopausal women — also experienced unusual
bleeding.
The new study — the largest to date — expands on
research that has highlighted the temporary effects of COVID-19 vaccines
on menstrual cycles but until now focused primarily on cisgender women
who menstruate.
Although the vaccines have largely prevented
deaths and severe disease with few reported side effects, many medical
experts initially brushed aside concerns when women and gender-diverse
people started reporting erratic menstrual cycles after receiving the
shots.
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To
get a better sense of these post-vaccination experiences, researchers
at the University of Illinois at Urbana-Champaign and Washington
University School of Medicine in St. Louis distributed an online survey
in April 2021 to thousands of people across the globe. After three
months, the researchers collected and analyzed more than 39,000
responses from individuals between the ages of 18 and 80 about their
menstrual cycles. All the survey respondents had been fully vaccinated —
with the Pfizer-BioNTech, Moderna, Johnson & Johnson vaccines or
another that had been approved outside the United States. And to the
best of their knowledge, the participants had not contracted COVID-19
before getting vaccinated.
The research, published Friday in the
journal Science Advances, shows that 42% of people with regular
menstrual cycles experienced heavier bleeding after vaccination, while
44% reported no change, and 14% reported lighter periods. Additionally,
39% of respondents on gender-affirming hormone treatments, 71% of people
on long-acting contraceptives and 66% of postmenopausal women
experienced breakthrough bleeding after one or both of their shots.
“I
think it’s important that people know this can happen, so they’re not
scared, they’re not shocked, and they’re not caught without supplies,”
said Katharine Lee, a biological anthropologist at the Washington
University School of Medicine in St. Louis and the study’s first author.
Lee
cautioned, however, that the study did not compare the results with a
control group of people who did not get vaccinated. And it is possible
that people who observed changes in their cycles after vaccination may
have been more likely to participate in the survey. Still, the findings
line up with smaller studies that have reported menstrual changes after
vaccination with more robust controls.
Importantly, the new study
also found that some demographics may be more likely to experience
menstrual changes, and the study may help them be better prepared, Lee
said. A heavier menstrual flow was more likely for those who were older,
for instance. Survey respondents who used hormonal contraception, had
been pregnant in the past or had been diagnosed with a reproductive
condition like endometriosis, fibroids or polycystic ovarian syndrome
were also more likely to have heavier bleeding during their periods.
People who identified as Hispanic or Latino tended to report heavier
bleeding too. And people who experienced other side effects of the
vaccines, like a fever or fatigue, also had a higher chance of
experiencing erratic periods.
Postmenopausal women who were
slightly younger, around an average age of 60, were more likely to
experience breakthrough bleeding after the vaccine than those who were
older. But the type of vaccine postmenopausal women received, whether
they had other side effects like a fever or whether they had a past
pregnancy did not seem to have an effect on their bleeding.
Why do these changes occur?
Some
level of variation in menstruation — the number of days you bleed, the
heaviness of your flow and your cycle length — is normal.
“Our
menstrual cycles are not perfect clocks,” said Dr. Alison Edelman, a
professor of obstetrics and gynecology at Oregon Health & Science
University who has also studied the effect of COVID-19 vaccines on
menstruation.
Hormones secreted by the hypothalamus, the pituitary
gland and the ovaries regulate the monthly cycle, and they can be
affected by both internal and external factors. Stress and illness,
weight loss or weight gain, calorie restriction, and intense exercise
can all change typical patterns of menstruation.
The endometrium,
which lines the uterus and is shed during menstruation, has also been
linked to the immune system. Because of the role it plays in the
remodeling of uterine tissue and offering protection against pathogens,
it is possible that when vaccines activate the immune system, which is
what they should be doing, they also somehow trigger downstream effects
in the endometrium, causing a disturbance in your menstrual cycle,
Edelman said. And some individuals may be more sensitive to immune or
hormone changes in their body.
In her research, Edelman found that
some women’s periods came a day or two later than usual after they got
vaccinated against coronavirus. But the changes were temporary —
menstruation tended to return to normal after one or two cycles.
What to do if you notice menstrual irregularities after the COVID vaccine
If
you experience any new or unusual patterns of bleeding, take note of
it. The menstrual cycle can be thought of as another vital sign, just
like your body temperature or blood pressure, that provides clues about
your health, said Dr. Jennifer Kawwass, a reproductive endocrinologist
at Emory University, who was not involved in the study.
“A
significant change in menstrual cycle interval or bleeding profile
warrants further investigation to be sure there is not an underlying
endocrinologic, hematologic or anatomic cause,” Kawwass said.
Breakthrough bleeding in people who no longer normally menstruate, for
example, may also be a warning sign of cervical, ovarian, uterine or
vaginal cancer.
That being said, subtle variation in your
menstrual cycle, if you have regular periods, should not be a cause for
concern and does not require that you change anything you would normally
do, Kawwass said.
Clinical trials and other studies have already
established that the COVID-19 vaccines are safe and effective and are
unlikely to affect fertility in the long term.
Should you get vaccinated at a certain time in your cycle?
Experts
agree that the chaos COVID-19 can cause throughout your body, including
potential lingering effects, is far worse than any side effects caused
by vaccination against the disease.
People who have previously
gotten a fever after a shot may plan their next dose on a day when they
will not have to go in to work, Edelman said. But you should not let
temporary menstrual changes prevent you from getting fully vaccinated or
boosted. Since cases are on the rise again, delaying vaccination for
two weeks or longer may significantly increase your risk of getting
COVID-19, she said.
Still, it’s important to track your body’s
response to vaccination, and public health officials should acknowledge
concerns about menstrual cycle variations in addition to warning people
of the risk of getting COVID-19, said Keisha Ray, a bioethics expert at
McGovern Medical School at UTHealth Houston.
The increased
transparency around menstrual changes or other side effects of
vaccination could also have another benefit: reducing people’s vaccine
hesitancy.
“We’re trying to be truthful. We’re trying to validate
people’s lived experiences,” Lee said. In turn, she hopes that the new
research will help improve conversations around people’s health and lead
to more inclusive clinical trials in the future.
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