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A Possible Side Effect? Thousands Of People Saw Menstruation Changes Post-Vaccine

MARY LOUISE KELLY, HOST:

Over half of eligible Americans have received a COVID-19 vaccine, and many have experienced common side effects - things like sore arms, maybe a fever. But some people say they have also had changes to their menstrual cycles. NPR's Geoff Brumfiel investigates.

GEOFF BRUMFIEL, BYLINE: Katharine Lee is an anthropologist at Washington University School of Medicine in St. Louis.

KATHARINE LEE: I was on the earlier end of getting vaccinated.

BRUMFIEL: Like a lot of people, she wondered about the side effects she might have - headaches, fevers, things like that. But after getting the shot, she experienced something she definitely was not expecting - a change to her period.

LEE: I'm on the Mirena IUD, so I normally don't experience a period. And so I had breakthrough bleeding and cramping, which for me is really, really unusual.

BRUMFIEL: The bleeding she experienced was spotting, not serious but uncomfortable. So she reached out to her colleague Kate Clancy, an anthropologist at the University of Illinois. It turned out Clancy had experienced an unusually heavy period after her vaccine, and she had a fairly large Twitter following.

KATE CLANCY: I just decided to ask, and I did not anticipate it blowing up to the extent that it has.

BRUMFIEL: She says people are still responding to a tweet she sent months ago.

CLANCY: A lot of emails, a lot of Instagram DMs and a lot of tweets of people who are, like, just baring their souls to us.

BRUMFIEL: Clancy and Lee put together a survey for people to record their experiences. So far, they've had over 140,000 responses. Many are reporting heavy flows, but others have seen changes as well.

CLANCY: We started hearing a lot about breakthrough bleeding from people on long-acting, reversible contraception, people on gender-affirming hormones and postmenopausal people who were years and years out from their last period, sometimes decades out.

BRUMFIEL: These stories are important, but they don't prove a connection to the vaccines. For one thing, Katharine Lee says they're told voluntarily by people who want to share their stories.

LEE: It's not going to be representative of the averages of everyone who's vaccinated.

BRUMFIEL: In other words, this is just a small fraction of the many tens of millions of people who've had a shot. And many have not reported problems. In fact, vaccine manufacturers and the FDA all say they do not currently see evidence that the shots are causing any changes to menstruation. Kathryn Edwards is a physician at Vanderbilt University. She sits on an independent data monitoring committee for the Pfizer vaccine. It's a paid position.

KATHRYN EDWARDS: We haven't really heard much concern about menstrual issues.

BRUMFIEL: She says if any menstrual problems were dangerous, she would know.

EDWARDS: If it were leading to hospitalizations and severe illness, we would catch that.

BRUMFIEL: But Edwards says if the changes to menstruation are relatively minor, they might be missed. Participants in clinical trials are handed a checklist to ask about minor side effects like headaches or those sore arms people get. But...

EDWARDS: There aren't any queries to say, are your menstrual periods irregular? You know, are you - is your flow heavier?

BRUMFIEL: In fact, the Centers for Disease Control and Prevention tells NPR it's now reevaluating its vaccine safety data to see whether it might be possible to spot any minor menstrual issues that they would have overlooked before. Laura Riley is a doctor and chief of obstetrics and gynecology at New York-Presbyterian Weill Cornell Medical Center. She says for anyone worried about all this, the data that's out there is actually pretty clear.

LAURA RILEY: You need to get vaccinated. The effects of getting COVID-19, especially with rising cases due to this variant, are so much worse than missing a period or having one or two that are heavy.

BRUMFIEL: At the same time, she says those who menstruate have a right to know whether a vaccine could have an influence.

RILEY: We need to do a better job of being able to answer those questions because when you can't answer the questions, you're asking people just to believe, and that's not a thing.

BRUMFIEL: Just knowing it's a side effect, even if it's no worse than a sore arm, will give people peace of mind.

Geoff Brumfiel, NPR News.

(SOUNDBITE OF VAGABON SONG, "MAL A L'AISE") Transcript provided by NPR, Copyright NPR.

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