COVID Shot Doesn't Affect Fertility, Changes to Period Short-Lived, Experts Say

Medical experts have said any effect that the COVID-19 vaccine has on periods seems short-lived, although a link between the two is not yet clear.

Dr. Kate Clancy, a medical anthropologist and professor at the University of Illinois, posted a series of tweets in February explaining that she had had a heavier-than-usual period about 10 days after receiving her first dose of the Moderna vaccine.

Her tweets attracted hundreds of replies and retweets—so Clancy and a colleague, Dr. Katharine Lee, began to put together a self-reporting tool to gather the experiences of other women.

A colleague told me she has heard from others that their periods were heavy post-vax. I'm curious whether other menstruators have noticed changes too? I'm a week and a half out from dose 1 of Moderna, got my period maybe a day or so early, and am gushing like I'm in my 20s again.

— Dr. Kate Clancy 🏳️‍🌈 (@KateClancy) February 24, 2021

Clancy and Lee have now shared the results of their survey with The Guardian's Science Weekly podcast.

They found that the experiences recorded varied widely. Clancy said some people, such as those taking hormonal contraceptives or gender-affirming hormones, reported "effectively surprise periods or breakthrough bleeding." Post-menopausal women also got in touch to report bleeding after the COVID vaccine.

Clancy added that some respondents reported experiences similar to hers, with early periods and heavier bleeding, while others said the opposite had happened. Some said nothing had changed at all.

Clancy said the changes that had been reported did not appear to last for long—"one to two cycles, max."

She suggested that a vaccine could potentially affect menstruation because inflammatory processes that drive the cycle could be inadvertently impacted by "a giant wallop of an immune event."

The link between COVID vaccines and the menstruation is not clear, however, and many other factors including stress can have an impact on cycles.

Pat O'Brien, a vice president of the Royal College of Obstetricians and Gynaecologists in the U.K., told The Guardian that many women were having the COVID vaccine and so "it seems inevitable that in some women these two events will coincide by chance." He added that people should see a doctor if the changes persist.

O'Brien also stressed that there was "no evidence to suggest that COVID-19 vaccines will affect fertility."

In April, Dr. Heather Huddleston, a specialist in reproductive hormones and infertility, made similar comments about the vaccine to ABC7 News: "There is no reason to think there's reason to be concerned over time, and there's no reason to think that there's any impact on fertility."

She likened the anecdotal evidence about changes to menstrual cycles to a sore arm—a vaccine side-effect that is a nuisance in the short term, but "is not a representation of any sort of permanent harm or damage."

Women should continue to get vaccinated, she added.

The idea that vaccines could be affecting periods has given rise to vaccine hesitancy and people spreading COVID vaccine misinformation online, including the false claim that cycles could be affected just by being near vaccinated people.

Newsweek, in partnership with NewsGuard, is dedicated to providing accurate and verifiable vaccine and health information. With NewsGuard's HealthGuard browser extension, users can verify if a website is a trustworthy source of health information. Visit the Newsweek VaxFacts website to learn more and to download the HealthGuard browser extension.

COVID vaccine
A person receives a COVID vaccine at the Jackson Memorial Hospital in Miami, Florida, in December 2020. The vaccine has no effect on fertility, experts have said. Joe Raedle/Getty