A fair few people across the world have been reporting an unusual experience: shortly after receiving their COVID-19 vaccine, they started to have irregular periods, more painful periods, or other changes to the menstrual cycle.
These anecdotal reports are not fully understood yet, but scientists suggest that it’s certainly plausible the vaccination may have a short-term effect on menstrual cycles. Rest assured, however, there is no evidence that the COVID-19 vaccine is going to mess with your fertility or reproductive health.
“If you’re eligible to receive a vaccine, then do so. And if you do have a heavier period next month, think of it like a temporary side effect, and try not to worry,” Michelle Wise, senior lecturer from the Department of Obstetrics and Gynaecology at the University of Auckland in New Zealand, recently wrote in the Conversation.
The scale of the issue isn’t clear, but there have been around 958 cases of post-vaccination menstrual irregularities as of April 5, 2021, according to UK government statistics cited in a letter to the British Medical Journal.
Dr Kate Clancy, an associate professor of biological anthropology who specializes in reproductive health at the University of Illinois, is looking to better understand the scale of the problem by asking volunteers to participate in an online survey about their experiences with menstruation after receiving a COVID vaccine.
Dr Clancy tweeted that she experienced an unexpectedly heavy period after getting the Moderna vaccine and received a stream of replies citing similar experiences, prompting her and a colleague to put together a self-report tool. She has also said a number of trans men and post-menopausal women who don't normally have periods have also reported unexpected bleeding after getting the COVID vaccine, according to BBC News.
The cause of this possible link is not certain either, but scientists have speculated that it is most likely to do with the role of the immune system in the womb lining. The menstrual cycle is, in part, mediated by the immune system with certain immune cells used in the process of shedding and rebuilding the lining of the uterus. It’s possible that the vaccine, which prompts a wider immune system response against COVID-19, may have some complex effect on the immune cells in the uterus, leading to slight changes in the menstrual cycle.
There have been reports that other people’s vaccines could disrupt menstrual cycles. In April 2021, a private school in Florida told teachers that they could not interact with students if they’d received their vaccine because “we have at least three women with menstrual cycles impacted after having spent time with a vaccinated person.” As the New York Times reports, there is zero evidence behind this particular claim.