No hard evidence exists that the coronavirus vaccines can lead to menstrual cycle irregularities. There are, however, anecdotal reports that some women experience temporary changes after vaccination, such as a missed period or a particularly heavy one. And some health experts believe it is plausible, although there is not enough research yet to prove it.
Still, health experts said that assuming menstrual cycle irregularities are associated with the vaccines, it could have something to do with the immune response to the shots or mental or physical stress associated with them.
After vaccination, an inflammatory response could occur in the lining of the uterus called the endometrium, which could affect menstruation for a short time, similar to other side effects of the vaccines, said Jane van Dis, assistant professor of obstetrics and gynecology at the University of Rochester.
Also, mental or physical stress can suppress the release of hormones from the brain that tell the ovaries and other endocrine organs in the body what to do, which could delay a woman’s period or temporarily alter the flow, said Andrea Edlow, assistant professor of obstetrics and gynecology at Harvard Medical School. She said that this may be more common for women who are prone to irregular periods.
In any case, Edlow said she doubts these menstrual disturbances are unique to the coronavirus vaccine.
“I think we’re seeing them reported because we’re in an unprecedented period of medical and scientific discovery right now, where people are seeking out information about novel vaccines and side effects,” she said. “But I suspect that if people have a menstrual disturbance from the covid vaccine, they easily could also have a menstrual disturbance from other vaccines and certainly from illness.”
So, yes, we know there are self-reported short-term menstrual changes in some women after vaccination, but we cannot know for certain that there is an association without more research.
And assuming there is a link, there is no indication that the vaccines would cause permanent issues with women’s cycles or fertility. (To be clear, the claim that the vaccines might lead to infertility is a myth.)
As for women who experience long-lasting issues with menstruation after vaccination, Edlow said they should see their doctor to be evaluated for other causes.