A big question that’s emerged recently is whether or not COVID-19 vaccines can affect the menstrual cycle after many people reported changes in their period timing, symptoms, and bleeding soon after getting the vaccine. Because the manufacturers of the COVID-19 vaccines on the market did not assess changes in the menstrual cycle during their clinical trials, we don’t yet have large-scale data about whether they may have real effects. (You can contribute to those research efforts here!) However, adds Dr. Jenn Conti, MD, MS, MSc, OB-GYN and Modern Fertility medical advisor: "When there are no data, we must listen to people's voices and lived experiences."
In this post, we’ll help you clarify what's important to listen to (and what's not) when it comes to COVID-19 vaccines, menstrual cycles, and fertility more generally. Here's the bottom line: Since we don’t have systematic data on COVID-19 vaccines’ effects on the menstrual cycle, we can’t be certain that any reported differences are a direct result of the vaccine. But if there *are* real vaccine-induced changes, we can be confident they’re only temporary — and we have no reasons or data to believe the vaccines impact menstruation or fertility in the long term.
Reminder: How do the vaccines work?
There are currently three vaccines that have received authorization for emergency use by the FDA:
- Two of the vaccines (Pfizer and Moderna) are mRNA-based, and one is DNA-based (Johnson & Johnson).
- In a nutshell, they all work by prompting your body to produce the spikey S proteins that are characteristic of the virus that causes COVID-19. Your body detects these S proteins and launches an immune response to eradicate them, and thus, acquires the immune response to eradicate COVID-19 if it were to ever enter the body.
- The main difference between the mRNA- and DNA-based vaccines is how they deliver the message to produce the S proteins, but at the end of the day, they rely on the same underlying logic.
Can the COVID-19 vaccine really impact the menstrual cycle?
In the absence of the kind of gold-standard studies we’d want to see on vaccines and menstrual cycle characteristics, we can first rely on our understanding of basic reproductive endocrinology and immunology to guess why there might, in theory, be links between vaccines and the menstrual cycle — though not necessarily direct ones.
As recently outlined by myth-buster and OB-GYN extraordinaire Dr. Jen Gunter, there may be a couple of ways the COVID-19 vaccine might be associated with altered menstrual function:
- The COVID-19 vaccine might affect compounds and cell types that change menstrual bleeding or timing. There are a couple of different compounds and cells that are involved in immune function that are also involved in menstruation. The uterine lining (aka endometrium) is part of the immune system, and the immune system is what gets put into overdrive after getting a vaccine (COVID-19 or otherwise). The immune system response to the vaccine could impact these compounds and cells, resulting in cycle changes.
- The stress of vaccination could affect hormone production and menstruation. Vaccination can be stressful — whether it be the act of going to the appointment, getting the actual vaccine injected, or worrying about if there will be side effects. Stress can alter the brain regions responsible for kick-starting reproductive hormone production. If stress is the culprit here, that means the potential link between vaccination and menstruation isn't a direct one.
- People might be paying more attention to their bodies after getting a vaccine because they may be anticipating side effects. Any changes in how they feel or physical things they experience could be attributed to the vaccine when in reality they might be completely unrelated. This point is especially salient in the world of menstruation, where it’s common to have considerable differences in cycle length and number of bleed days from cycle to cycle.
Dr. Jane van Dis, MD, FACOG, an OB-GYN at OB Hospitalist Group and a Modern Fertility medical advisor, tells us that all of those links are possible, but adds: “As a frontline healthcare worker who saw the devastating effects of COVID firsthand, are we going to focus on the possibility of a change in your cycle over one or two months or the actual human deaths and suffering COVID infection caused and is still causing?”
From Dr. van Dis’ perspective, the media is conflating the very real and important exclusion of the possible experiences of people with ovaries in vaccine trials with evidence of something inherently “nefarious.” People may feel discouraged from getting vaccinated because of this info and be more vulnerable to the known complications that may stem from infection.
Should you be concerned if your cycle changes after getting vaccinated?
According to Dr. Conti, the answer to this question depends on your circumstances. "For someone having regular, monthly cycles, this will likely right itself on its own in time," she says — but any bleeding after menopause warrants a biopsy to rule out uterine cancer. (Important reminder here that vaginal bleeding is only your period when it's preceded by ovulation.) One of Dr. Conti's patients recently experienced postmenopausal bleeding after getting vaccinated: "Would it have happened if she didn't get the vaccine? Maybe, but we don't really know yet," Dr. Conti says. "If we had this guidance ahead of time, we could potentially avoid some uncertainty."
Like Dr. Conti explains, any noticed changes to your regular menstrual patterns post-vaccine should be temporary:
- The immune system response is rapid but quickly subsides (which is why it’s normal to have symptoms for a day or two post-vaccine, but not beyond that).
- If it really is interactions between the immune system and endometrium that explain links between the vaccines and menstruation, we wouldn’t expect to see them for more than that first post-vaccine period.
- The same goes for stress — if it was the stress of vaccination that affects menstruation, we’d expect things to go back to normal once this stress subsides.
- Importantly, if you're menopausal and haven’t had a period for over a year, be sure to talk to your doctor if you experience vaginal bleeding after a COVID-19 vaccine. Post-menopausal vaginal bleeding can be a sign of pre-cancer or cancer and misattributing it to the vaccine could delay diagnosis. (And no, the vaccine can't trigger periods to return after menopause.)
Even outside the context of vaccines, menstrual cycles often vary for a multitude of reasons. That said, if you start noticing any extreme changes in how often you’re getting a period, how many bleed days you have, or how much you are bleeding, it’s best to reach out to your doctor.
Can being around someone who got a COVID-19 vaccine impact your menstrual cycle?
This one's a hard no: "Shedding" a vaccine isn't a thing — just like how being around a vaccinated person won’t magically give you COVID-19 antibodies.
In an April 2021 article published in the New York Times, Emily Martin, an infectious disease epidemiologist at the University of Michigan, explains the science of vaccination this way: “It’s not like it’s a piece of the virus or it does things that the virus does — it’s just a protein that’s the same shape. Transferring anything from the vaccine from one person to another is not possible.”
While you may have seen this myth pop up recently, it's very likely the people promoting it are doing so to discourage vaccination — not because they've found a science-backed reality the medical community at large is ignoring.
Friendly reminder: There's no scientific evidence that the vaccine impacts fertility
- Neither the Centers for Disease Control and Prevention (CDC), the American College of Obstetricians and Gynecologists (ACOG), nor the Society for Maternal-Fetal Medicine (SMFM) have cautioned against getting the vaccine for people who may want kids now or in the future. In fact, the CDC recommends the vaccine for pregnant people.
- ASRM’s official statement says: “The Task Force does not recommend withholding the vaccine from patients who are planning to conceive, who are currently pregnant, or who are lactating.”
- Although no studies have specifically looked at the impact of the vaccines on fertility, based on the vaccine's mechanism of action, experts say there's little to no evidence of adverse effects.
- Several people got pregnant in the original Pfizer vaccine trials — meaning the vaccines don’t inhibit your ability to do so.
- There were also no noted effects on fertility in animal trials conducted before the vaccines were approved for testing in humans.
Like with anything related to COVID-19 or the FDA-authorized vaccines, we'll have more conclusive answers as time goes on and as more research is conducted. (And if you're curious about how many pregnant people in the US have been vaccinated, the CDC is keeping track: As of early May, it was over 100,000 pregnant people.)
Bottom line: We need more info
What we’re seeing here is something seen all too often in the world of clinical trials: Effects of treatments and vaccines on menstrual function are not assessed, leaving us with a stunning lack of information about what to expect.
Researchers are taking the issue into their own hands, and we’ll soon have a better understanding of associations between the COVID-19 vaccines and menstrual characteristics.
Any menstrual changes observed post-vaccination are temporary, and there’s no evidence the vaccines have long-term effects on menstrual function, fertility, or pregnancy and birth outcomes.
This article was medically reviewed by Dr. Jane van Dis, MD, FACOG.