Katharine Lee received her COVID-19 vaccination early in the United States’ entry into force. So did a friend of hers – they got their shots the same day. They compared notes, curious to see what the side effects would be. Lee, a research fellow in the Division of Public Health Sciences at Washington University in St. Louis. Louis, says they both had one surprising symptom: they both started their period shortly after taking the vaccination.
“It was not a symptom that was on the list,” she says. “I expected my arm to hurt, or I would have a fever or a headache, but it just wasn’t on the list.”
Lee reaches out to Kate Clancy, who is studying the menstrual cycle at the University of Illinois, to share the observation. When Clancy got her vaccination, she also had an unusual period. That’s why she posted on Twitter asking if other people did the same – and watching dozens of responses roll in.
A colleague told me that she had heard from others that their periods were heavy after growing up. I’m curious if other menstruators have noticed changes as well? I’m a week and a half out of dose 1 of Moderna, got my period maybe a day or so early, and I’m getting into my 20s again.
– Dr. Kate Clancy ️ (@KateClancy) 24 February 2021
“It made us want to capture these experiences,” Lee says. So this week, the couple began a formal study to gather data on the link between the COVID-19 vaccines and the menstrual cycle. It is not a side effect after which clinical trials have been tested, and it is not included in the Centers for Disease Control and Prevention of the vaccine’s health information.
There is not much research on how the vaccine affects menstruation. But vaccines do stress the immune system, and the menstrual cycle sometimes responds to such changes. “The menstrual cycle is really dynamic and responds to a lot of things,” Lee says.
There is also a possible link between the nanoparticles used in the COVID-19 vaccines and changes in bleeding patterns. In some people, the nanoparticles eventually create a temporary immune response that kills platelets, a type of blood cell involved in clotting, Clancy says. They regenerate quickly, but if someone has a bleeding like a period just after getting a shot, it can get heavier. She will be collaborating with Anirban Sen Gupta, a platelet researcher at Case Western Reserve University, to try to understand the potential mechanism.
If there appears to be a link between the vaccines and the timing of a person’s menstrual cycle, it does not mean that there is something wrong or dangerous with the vaccines. Lee is likely to have a temporary side effect and is unlikely to affect its fertility. It would not be as different from other side effects that the vaccines cause, such as fever or headache. But it is important to thoroughly understand what reactions the vaccinations can cause, so that people are as informed as possible about what they may be experiencing.
“It’s really hard to be surprised by your period,” says Lee. “It’s nice to know it can happen, just like knowing you have a fever and a headache.”
Similarly, unusually heavy periods are usually something people should be concerned about – it could be a sign that something is wrong, says Clancy. Knowing that it is a possible effect of the vaccine may make the experience less worrying. On the other hand, if the research shows that there is no strong link with vaccination, it could mean that people who have this experience should go to the doctor to make sure there is nothing else wrong.
People are eager to share their stories about this survey, Clancy says. Within a day after the survey was launched, there were already more than 700 responses. They hope to better understand how people’s periods change and what are the characteristics of people who experience these experiences – their age, gender, underlying health conditions or other factors. They also keep track of the timing. Clancy says she suspects that people who get the chance just before their period is supposed to start are more likely to see heavy bleeding.
At the moment, Lee says they hope the survey fills a knowledge gap around menstruation and the vaccines. People discussed their experiences on social media, but it did not appear in any scientific literature. Lee says she’s not surprised. It took until the 90s before women were regularly admitted to clinical trials of any kind, and some of the persistent prejudices remain.
“These are not things that some people think about. It is not part of their daily experience. I think a lot of it has to do with that history, and the prejudice around who has to decide what is important to consider as a side effect, ”she says.