Do covid vaccines affect periods? A new study says yes.

Shortly after the coronavirus vaccines were launched last year, women across the country began posting on social media what they believed to be a strange side effect: changes in their periods.

Now, new research shows that many of the complaints were valid. A study of nearly 20,000 people worldwide shows that getting vaccinated against covid can change the timing of the menstrual cycle. Vaccinated people experienced, on average, a one-day delay in getting their periods, compared to those who had not been vaccinated.

The study data, published Tuesday in the British Medical Journal, was taken from a popular period-tracking app called Natural Cycles and included people from around the world, but most were from North America, Britain and Europe. The researchers used “de-identified” data from the app to compare menstrual cycles between 14,936 participants who were vaccinated and 4,686 who were not.

Because app users tracked their menstrual cycles each month, the researchers were able to analyze three menstrual cycles before vaccination and at least one cycle after, and compare them to four menstrual cycles in the unvaccinated group.

The data showed that vaccinated people had their periods 0.71 days late, on average, after the first dose of vaccine. However, people who received two shots within one menstrual cycle experienced greater interruptions. In this group, the average increase in cycle length was four days, and 13% experienced a delay of eight days or more, compared with 5% in the control group.

Alison Edelman, a professor of obstetrics and gynecology at Oregon Health and Science University, who led the study, said that for most people the effects were temporary, lasting for one cycle before returning to normality He said there was no indication that period side effects had any impact on fertility.

“Now we can give people information about what to expect with menstrual cycles,” Edelman said. “So I hope that overall it’s very reassuring for people.”

Researchers don’t know exactly why vaccines seem to affect menstrual cycles, but Edelman said the immune and reproductive systems are linked, and inflammation or a strong immune response could cause menstrual fluctuations.

Any change in menstruation can be stressful, leading to worries about an unplanned pregnancy or illness, and people have expressed frustration that public health officials didn’t warn them about the potential side effect or do more research before launching the pills. vaccines

A major limitation of the study is that it included only those who were not on birth control, had regular cycles before getting vaccinated, and were between the ages of 18 and 45.

The study also didn’t answer all the questions people had about vaccines and periods, including how the shots affect trans men and non-binary individuals. Since the vaccines were launched, many people on social media have complained about longer, heavier and more painful periods after getting the shot. That study didn’t look at period heaviness or other side effects like cramps, but the researchers said it did show that, on average, getting vaccinated didn’t seem to cause longer periods.

Edelman said preliminary findings from a different study suggest that getting a coronavirus vaccine can sometimes lead to heavier periods. The data, collected from nearly 10,000 people, is still undergoing peer review, but showed that getting vaccinated slightly increased the likelihood of heavier bleeding.

However, she acknowledged that her studies have only looked at people with normal menstrual cycles who are not using hormonal contraceptives, and that individual experiences can vary widely.

Caiityya Pillai, 21, who lives in Berkeley, California, said that for two months after her injection in March 2021, her normal light period became extremely painful and lasted twice as long.

“The pain wasn’t like normal pain. It was to the point where I cried and couldn’t get out of bed,” she said.

Pillai said she was overwhelmed with anxiety and thought something else might be wrong, but after two cycles, her period returned to normal. When she received a second dose in July 2021, her period got worse again, but she said she felt more reassured because she had seen similar stories shared online.

Other research has suggested that vaccines have several effects on periods. A survey published last fall collected period and vaccine information from 160,000 people, including transgender and postmenopausal women, and found that thousands reported heavier-than-usual bleeding or breakthrough bleeding.

While these observations aren’t necessarily medically alarming, Katharine Lee, an assistant professor at Tulane University who led the survey, said the information is important to help trans men plan for additional support if menstruation causes dysphoria of gender and also to help them. people make decisions about stocking up on tampons and pads.

Lorena Grundy, 27, uses an IUD and hadn’t had a period for more than three years before getting her first shot from Pfizer in February 2021. The next day at work, she got her period.

“It wasn’t that the vaccine moved my period earlier or later, it just produced one,” said Grundy, who lives in Somerville, Massachusetts.

Had she been aware of the side effect, she said, she would have prepared and brought a pad to work. Her period lasted three to four days, and returned when she received her second dose of vaccine three weeks later. But it didn’t happen again when he got a booster shot last November.

“I think it’s good to validate that we need to listen to women about their own bodies,” she said. “I’m still glad I got vaccinated, but I think maybe this shows it’s a symptom we should be preparing people for so they don’t panic.”

Although Edelman’s research suggested that period changes are temporary, some people have reported lasting changes in menstrual cycles long after receiving a vaccine.

Sammi Beechan, 32, of Hammond, Ore., said they used to have a “beautiful, blessed cycle” that came every 28 days “like clockwork” and resulted in mild cramping and just four days of light to moderate bleeding.

After a shot from Johnson & Johnson in April 2021, nothing changed, but after receiving a booster from Moderna that October, Beechan noticed her period started coming every 24 days with more than four days of bleeding more intense, more painful cramps and extreme mood swings. . Doctors have ruled out endometriosis and other potential health problems as the cause.

Beechan said it’s worth getting the covid vaccine, but they wish more information about side effects had been provided in the period before the vaccine was released. “I went from having very constant expectations and now every month I’m like, OK, I guess this is what it is,” Beechan said.

Diana Bianchi, director of the Eunice Kennedy Shriver National Institute of Child Health and Human Development, which funded Edelman’s research, said having a significantly late period after vaccination is not necessarily cause for alarm.

“I wouldn’t recommend going to the doctor after the first time it happens, just because all the evidence is that the change resolves, it’s just temporary,” he said. “If it’s a persistent change in menstrual cycle interval, that might be a reason to see your primary care or OB/GYN doctor.”

The National Institutes of Health has funded at least four other research projects around coronavirus vaccines and menstruation, some of which are studying teenagers and people with endometriosis, hoping to provide better information and increase confidence of the public on vaccines.

Olivia Rodriguez, 26, said she doesn’t plan to get the booster shot because she had such a bad experience after her second Moderna shot in March 2021. Despite finishing her period, she started another a few days after receiving the vaccine. . It lasted 10 days with heavier bleeding, she said, instead of the normal four or five days she was used to. She also experienced more painful cramps.

At first, she panicked, but soon found stories online of other women who had been through similar situations. It was reassuring, he said, but he’s still wary of getting another shot.

Rodriguez, who is a member of the Osage Nation, said medical researchers need to gain the trust of Indigenous people and people of color by providing more information beforehand about side effects.

“I’ve never had an explanation of why or what happened,” he said.

correction

An earlier version of this article reported an incorrect number of respondents in a survey about periods and coronavirus vaccines. The survey collected information from 160,000 respondents, not 16,000. The article has been corrected.

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