When adults gained access to Covid vaccines last year, most knew to expect headaches, fatigue and aches as side effects.
But some researchers think it’s time to add another common one to the list: temporary menstrual changes.
An analysis published Friday in the journal Science Advances found that 42% of people with regular menstrual cycles reported bleeding more heavily than usual after vaccination. Meanwhile, 44% reported no change and about 14% reported a lighter period. Among nonmenstruating people – those post-menopausal or using certain contraceptives long-term, for example – the study suggests that many breakthrough or unexpected bleeding were experienced after their Covid injections.
The survey looked at more than 39,000 people aged 18 to 80 who were fully vaccinated and had not contracted Covid. The study authors cautioned, however, that the percentages do not necessarily represent the rate of menstrual changes in the general population, as people who observed a difference were more likely to participate. The purpose of the investigation was simply to provide evidence for future studies, not to establish a causal link.
Yet other recent research has also found that the Covid vaccine is associated with a small change in menstrual cycle length.
The new survey began in April 2021, around the time people started reporting unexpected bleeding and higher flow after the vaccine. However, these anecdotes were met at the time with the refutation that there was no data linking menstrual changes to vaccination.
It was both true and indicative of a larger problem. People who took part in the Covid vaccine trials were not asked if they had experienced menstrual changes.
“Before the vaccines came out, I would say our knowledge about the link between vaccination and menstrual changes, in general, was zero,” said Candace Tingen, program director in the Gynecological Health and Diseases Branch of the University. National Institute of Child Health and Human Development. Tingen did not participate in the recent investigation.
Overall, few studies assess the direct effect of vaccination on the menstrual cycle, and most pharmaceutical trials did not include questions about changes in menstruation.
Tingen considers this a mistake. Perhaps, she said, if the Covid-19 vaccine trials had asked about menstruation, people wouldn’t have been surprised — or scared — by this unexpected side effect.
“It’s really that lack of information that I think has caused confusion, fear and perhaps vaccine hesitancy,” she said.
Study co-author Katherine MN Lee said that overall, menstruation is understudied when it’s not relevant to pregnancy.
“It’s being ignored because of the structure of science,” said Lee, an assistant professor at Tulane University. “There are very few senior managers in science and medicine who are not white men. It’s just not something they think about as part of their lived experience.
Lee and his colleagues were inspired to ask people about their menstrual cycles after being vaccinated after seeing friends and strangers online wondering why they had experienced an unexpected change.
The survey group included more than 3,500 people who identify as gender diverse. About 84 percent of the participants were Caucasian, and none were between the ages of 45 and 55, because the researchers didn’t want to include changes associated with perimenopause, when the body begins the transition to menopause.
Respondents were vaccinated with Pfizer, Moderna, AstraZeneca, Johnson & Johnson and Novavax.
The group included people who usually don’t get their period because they’re post-menopausal, use long-acting reversible contraceptives or hormonal contraceptives, or are on gender-affirming treatment that stops menstruation. . A majority of these respondents had breakthrough bleeding after the vaccine.
Of the 238 postmenopausal people in the study who were not on hormone treatments and had not bled for at least 12 months before their vaccination, 66% reported breakthrough bleeding.
The survey found that, in general, people who had more flow after their injections were more likely to be non-white and older; use hormonal contraception; have a diagnosed reproductive problem; having also experienced fever or fatigue as side effects; or have been pregnant in the past.
As part of the survey, the team also included free response sections where participants could share their experiences.
“A lot of people have reported feeling like, ‘I’m so mad I didn’t know it beforehand, but I’m glad I got it anyway,'” said Kathryn Clancy, associate professor of anthropology at the University of Illinois and the other co-author of the study. “They wouldn’t have changed their decision to get vaccinated, but they felt betrayed that no one had told them to expect it.”
It is not yet understood why menstrual changes occur after vaccination. Tingen said the answer likely stems from the overlap between the immune system and the endocrine system, which plays a role in reproduction. (There are immune cells in the uterus that help during the process of menstruation, for example.)
“Diet, sleep, and stress can all affect the menstrual cycle,” Tingen said. “It is perhaps unsurprising that a large immune reaction can temporarily interrupt menstruation, in a minor way.”
Covid itself has been shown to disrupt menstruation more significantly than vaccines. This may be due to an ongoing immune reaction and the lifestyle changes that accompany the disease. People with long-term Covid are particularly affected, Tingen said, and more research into why is needed.
Menstrual changes as a side effect of the vaccine are comparable to others like muscle aches: Although they are uncomfortable, they do not change the safety or effectiveness of the injections. But Clancy said unexplained side effects scare people – and in some cases spread vaccine hesitancy.
Some vaccine skeptics have falsely confused the possibility of short-term menstrual changes with long-term damage to fertility, a message that Lee described as an “active misinformation campaign.”
Clancy said she had received messages from parents who had heard of menstrual changes and were concerned that vaccinating their child could cause precocious puberty, even though there is no evidence of this.
According to the study, post-vaccine surprises posed particular challenges for trans men and genderqueer people, as some had to navigate public restrooms or the workplace after experiencing unexpected periods.
“Unexpected bleeding poses a risk of psychological distress for those with gender dysphoria with menstruation and physical harm for those for whom managing menstruation in public is dangerous,” the authors wrote.
Clancy, Lee and their colleagues hope their work will inspire new research, encourage clinicians to talk to patients about the link between vaccination and menstrual changes, and validate people who have felt ignored or alone in their experiences.
“If you want to improve trust in government, trust in pharmaceutical companies, trust in medicine, trust in vaccines, then you have to take the time to do the work, so people know what they’re up to.” wait,” Clancy said. “This effort makes people more likely to get their second shot or booster.”
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