The COVID-19 vaccines have been tested extensively, but some people still have questions about how they will affect their lives. For instance, have you heard that the COVID-19 vaccine could affect your period? In this blog post, we’ll discuss the research-based answer to this question, but the short version is no. There isn’t evidence that any COVID-19 vaccines that have been approved for emergency use will affect your period. Read on to learn more.
The first thing you should know is that COVID-19 infection has been shown to affect menstrual cycles. In one study published in January 2021 in the journal Reproductive biomedicine online, gynecologist Kezhen Li and colleagues at Huazhong University of Science and Technology in China found that more than a quarter of 237 patients with COVID-19 infection experienced changes to their menstrual cycles, including a lower volume of blood and a longer lasting cycle.  Epidemiologist Leslie Farland and colleagues at the University of Arizona showed in a study published in the American Journal of Obstetrics and Gynecology in September 2021 that 16 percent of their 127 study participants noticed a change in their menstrual cycles during or after COVID-19 infection. 
Until recently, though, the question of whether or not COVID-19 vaccination affects menstruation had not been explored in depth. Enter Victoria Male, an immunologist with a focus on pregnancy who does research at Imperial College London. Male recruited 250 participants who were tracking their periods before they received either AstraZeneca, Moderna, or Pfizer COVID-19 vaccines and 1,273 people who had already received a COVID-19 vaccine, were tracking their periods, and want to discuss their experience with researchers.
In November 2021, she published her preliminary results in medRxiv, a so-called preprint server where researchers can release their science before it’s been peer reviewed.  Because the research has not yet been reviewed by other scientists, it’s possible that some of the interpretations will be different when the paper is published in another journal. At the same time, the research is a good starting point for understanding whether or not vaccination affects menstruation, so worth discussing here.
The first thing that Male found was that brand of vaccine had no effect on likelihood of reporting a change in menstrual cycle. This suggests that any link that might exist would be due to the immune system’s reaction to the vaccine, not to anything in the formulations of any of the three approved vaccines. She also determined that whether people were on birth control or not did not make them more or less likely to see changes to their menstrual cycles. Finally, most people didn’t see a change in cycle length or volume of flow post-vaccination.
The only populations in which Male observed a potential change were people with polycystic ovarian syndrome (PCOS), who were slightly more likely to have a late period, and endometriosis, who were slightly more likely to have an early period. In a Twitter thread about the paper, Male wrote, “if you have endometriosis or PCOS, I would still recommend getting vaccinated! Remember that COVID itself can mess with your cycle.” 
On Twitter, Male pointed out that her study is on the small side, and not yet complete. She also highlighted other research that’s ongoing from other groups who are looking at this same issue. That said, based on what researchers know right now, COVID-19 infection is much more likely to affect your menstrual cycle than the vaccines that have been approved for emergency use. If you’ve not yet been vaccinated, it’s a great time to read more about the vaccines (The Pulse is a great place to start) and talk to your care provider about protecting yourself from COVID-19.
- Li, K. et al., “Analysis of sex hormones and menstruation in COVID-19 women of child-bearing age,” Reproductive biomedicine online,
- Khan, S.M et al., “SARS-CoV-2 infection and subsequent changes in the menstrual cycle among participants in the Arizona CoVHORT study,” American journal of obstetrics and gynecology, 2021.
- Male, V., “Effect of COVID-19 vaccination on menstrual periods in a retrospectively recruited cohort,” medRxiv,
- Male, V. @VikiLovesFACS, (2021, November 15), “If you have endometriosis or PCOS, I would still recommend getting vaccinated! Remember that COVID itself can mess with your cycle. . .”