Did Covid-19 Vaccines Affect Women's Periods?

A large survey found temporary changes to the menstrual cycle in the aftermath of Covid-19 vaccination...
02 August 2022

Interview with 

Katharine Lee, Tulane University & Kathryn Clancy, University of Illinois


A cartoon representation of a uterus and ovaries


Across the globe, over 12 billion doses of coronavirus vaccines have been administered. And while potential side-effects of a sore arm, fever and fatigue were widely publicised, one impact not originally on the list started to crop up repeatedly: women reported short-term changes to their periods. But were these women who would have experienced this by chance anyway and it coincided with them getting the vaccine, or was there really a link? To find out, researchers have been poring over thousands of survey responses to better understand how vaccines might impact on periods. Julia Ravey spoke to Kathryn Clancy and Katharine Lee, who were behind the study…

Katharine - I am Katharine Lee.

Kathryn - ...and I'm Kathryn Clancy.

Julia - When did these reports start to come out about changes to people's menstruation? When did you start to notice them?

Katharine - I started to notice it after I got vaccinated in January of 2021. As someone who already researched periods, I was attuned to the fact that periods respond to tons of things, including an immune response, like the vaccine kicks off in your body. And so I personally experienced this and reached out to Kate to just ask if she'd heard anything similar from anyone else.

Kathryn - It's frankly because Katie noticed it to begin with that, when I finally got my vaccine a few weeks later and then my period another week and a half after that, I was having the heaviest period of my life. I asked Twitter, because of course that's what one does, if anyone else has had the same experience and the response was overwhelming.

Julia - Why was it hard initially to say the vaccine itself was having these impacts and what were some of the initial responses from doctors in the medical community to these claims?

Kathryn - The tweet went viral and our survey was very popular. So a lot of journalists wrote stories about the work that we were trying to do to capture these experiences. And almost every single article, with only a few exceptions, had a quote by an MD that either said there's no biological mechanism to explain this or these are ladies just experiencing pandemic stress and stress affects the menstrual cycle, too. Doctors and medical workers are going through a lot right now and I know they just wanna see people vaccinated - we all do. But the step to getting people comfortable with medical treatments, especially ones that have emergency authorisations, is to listen to them, right? And to make sure they feel heard and to have done the due diligence during the trials to make sure that we're understanding how different bodies react to the vaccine. These trials didn't ask any questions about menstruation at all.

Julia - Yeah, and if it wasn't reported on in the trials, I'm guessing that with your mission to try and understand a bit more about if there was a link between the vaccine and changes to menstrual cycles, you were starting with a bit of a blank slate then in terms of you have all these individual stories. But how did you go about collate them together to understand if there was a real link there?

Katharine - We designed our survey to ask about people's experiences with the period after their vaccine, in relation to their period that they would normally expect, or their lack of period for those who normally don't menstruate. And then we asked them, after dose one and after dose two, we just asked about those two periods, after each of those vaccines. It was the texture and content of their periods that was worrying for a lot of people. So it was heavier, or it was unexpected. We heard from a lot of folks who are trans or non-binary who suppressed their menstrual cycles in order to confirm their gender. And we did hear from a number of folks who experienced breakthrough bleeding, who had gender dysphoria as a result. So I think being aware that this is a possibility is important, especially for those groups, because making sure they have supplies on hand, making sure they are mentally and emotionally prepared as best as they can in case it happens is really important.

Julia - And did you find any particular relationship? So say for individuals who have certain conditions, were they more likely to experience these changes following having the vaccine into their periods?

Katharine - So there are a couple of things. We noticed that again, if anyone in the vaccine trials knew anything about the uterus, they might have kind of noticed and predicted this. But there were a couple of major trends that we saw. So among menstruating people, we saw that if they were a little older, if they had been pregnant before or had children, or if they had reproductive conditions that are hyper proliferative, so those are things like endometriosis or fibroids. People with those types of reproductive backgrounds were more likely to say that they had a heavier period. Among the postmenopausal folks, they were more likely to be younger as you might expect, because that probably means that their uterus is a little less quiescent or less old. So that uterus is maybe a little more likely to respond to the treatment. The uterus being the immune organ that it is, and the way that immune function is actually very tied up in blood, because blood is gonna be carrying all sorts of important things we need. It's got repair processes, it's got healing processes, it's got bleeding and clotting that it does. And that's all a natural thing that the uterus does regularly. And so you can imagine if you activate the immune system in some way, then that whole bleeding and clotting and inflaming and healing system is going to potentially be impacted by that.


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