Do COVID-19 Vaccines Affect Menstruation?

Dr. Paul Offit describes the findings of studies looking at the impact of COVID-19 vaccine on a woman’s menstrual cycle, including the relative timing of changes and vaccine receipt and other factors that may contribute to changes in the monthly cycle. He also discusses the findings as they relate to concerns about COVID-19 vaccines and fertility, which have not been demonstrated in these or other studies.


Do COVID-19 vaccines affect menstruation?

Paul Offit, MD: Hi, my name is Paul Offit. I'm talking to you today from the Vaccine Education Center at the Children's Hospital of Philadelphia. It's Friday, December 9th, 2022. So, one issue that's come up because it's been reported to the Vaccine Adverse Events Reporting System is, could these COVID vaccines, the mRNA vaccines or the Johnson & Johnson vectored virus vaccine, affect menstruation?

And the answer is, yes but slightly. So, this has recently been studied well to try and answer that question, could that happen? And what they found was that for the mRNA vaccines, it is possible that you could delay, or prolong, menstruation by 0.5 to 0.75 days. So, in other words, less than one day that you would delay, or prolong, the menstrual cycle by less than one day after the first dose.

It was also found that if you got the second dose within a cycle, that it was possible that you could delay the menstruation by as long as four days, remembering that there's always variability at some level in the number of days of menstruation and when menstruation starts. But I think that study answered the question, yes, it's possible, but it's really only less than a day after the first dose, and if you happen to get that second dose within a cycle, it could be as long as four days. But remember that this is a stress. I mean, anytime that you get a vaccine, you're inducing an immune response, that's a certain level of stress. So, that can happen in many different settings. It can happen arguably with other vaccines. It can happen with any sort of stress in one's life.

I think the more important thing is, does that matter? I mean, does that in any way affect fertility, for example? And it doesn't. I mean, that's clear. There have now been excellent studies looking at women who either did or didn't get this vaccine to answer the question, were they less likely to conceive a child? No. Also studies have been done looking at women who were pregnant who received this vaccine to see whether or not there was any difference in outcome either during the pregnancy or as far as the neonate was concerned, and there was no difference. So, women who get a vaccine during pregnancy have no complications of the pregnancy or no problems with the outcome of the child any different than a woman who was pregnant who didn't get the vaccine. So, quite the opposite, I think what you found now is that women who are pregnant and get the vaccine are less likely, much less likely to be hospitalized or go to the intensive care unit, and they are much more likely then to help protect their baby because they will passively transfer antibodies to the baby. So, that's why it's important for pregnant women to get vaccinated because they are at increased risk of being hospitalized or dying of COVID-19.

So, I think all in all, the news is good. It's certainly understandable that women could be concerned about this. And I guess the summary is that while the vaccines can affect menstruation slightly, it's all resolved by that second cycle. So, anything that happened in the first cycle is not seen in the second cycle. So, it's a trivial, short-lived problem and has no effect on the ability to get pregnant or no effect on the unborn child.

Thank you.

Related Centers and Programs: Vaccine Education Center

Last Reviewed on Dec 20, 2022